A native weevil and an exotic planthopper: investigating potential biological control agents for nymphaea mexicana zuccarini (nymphaeaceae) and its hybrids in South Africa
- Authors: Reid, Megan Kim
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422554 , vital:71957 , DOI 10.21504/10962/422554
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an invasive plant originating from southern USA and Mexico that has become problematic in South Africa, invading several water bodies around the country. Manual removal of this plant is very labour intensive and is not cost efficient or effective for long term control, while the use of herbicides is damaging to the environment and expensive. Consequently, this plant is a desirable candidate for biological control, which takes advantage of enemy release of the target weed and aims to re-establish population suppression induced by host specific natural enemies. Initiating biological control requires that several steps are followed to maximise the success of the programme, and the first few of these, including overseas surveys in the native range of the plant, have already been completed. This thesis aimed to continue biological control research for this species to take further steps at effectively managing the plant. Firstly, pre-release surveys in the invaded range are necessary to: determine what factors (including enemy release) contribute to the invasiveness of the target weed; establish a baseline of information to allow for comparison after biological control agents have been released; and identify any insect herbivores that may already be present in the country. The pre-release surveys conducted in this study revealed useful information about N. mexicana invasions in South Africa and provided evidence that enemy release is applicable to this case. However, these studies determined that a native weevil, Bagous longulus Gyllenhal (Coleoptera: Curculionidae), has expanded its host range to include the exotic N. mexicana at three sites, and may thus have potential for management of the species through augmentative releases. The invasion of N. mexicana in South Africa is further complicated by the presence of several Nymphaea hybrids originating from a complex history of horticultural trade. Although previous research has shown that several hybrid groups are present in South Africa, their parentage is not known. As biological control requires the use of host specific insects adapted to overcome the unique chemical and morphological defences utilised by plant species, hybrids are notoriously difficult to manage because they possess intermediate characters inherited from parent species to which natural enemies may not have adapted. Although biological control of hybrids is challenging, other case studies have demonstrated that it is possible to find suitable agents, but the chances of success are increased if putative parents of the hybrids are known so that they can be surveyed for natural enemies. Further molecular studies including possible parents of the Nymphaea hybrids in South Africa were thus carried out in this thesis to focus future surveying efforts. Two main hybrid groups were identified with genetic similarity to two tested putative Nymphaea parents, and this will allow further investigations of these species to improve the chances of successfully managing these hybrid groups. Some of the tested hybrids showed genetic contributions from multiple groups, some of which were unidentified, so it is necessary to prioritise the most problematic hybrids for biological control. With more insight into the genetic makeup of the Nymphaea hybrids in South Africa, investigations into the host specificity of potential biological control agents can be conducted. The ideal biological control agent should have a broad enough host range to impact and survive on both N. mexicana and its hybrids, but without a host range so broad that it would pose risk to native South African species. Host specificity trials are thus necessary to determine the suitability of potential agents. The identification of B. longulus feeding on N. mexicana during pre-release surveys motivated further investigations to determine the natural distribution, field host range, and host specificity of B. longulus in experimentally controlled conditions. Further surveys were therefore conducted at native Nymphaea sites around South Africa in addition to host specificity trials using the native Nymphaea nouchali Burm. f. (Nymphaeaceae), two populations of N. mexicana, and a cultivated hybrid. Results from the surveys and host specificity tests suggest that B. longulus is widely distributed across South Africa, is specific to Nymphaea with no observed preference between N. mexicana and the native N. nouchali, and does not perform well on Nymphaea hybrids. Hence, B. longulus is promising for use in new association biological control through augmentative releases but is not suitable for management of hybrids. In addition to the potential use of the South African B. longulus, it is necessary to conduct host specificity trials for natural enemies from the native range of N. mexicana that were prioritised in previous studies. Megamelus toddi Beamer (Hemiptera: Delphacidae) is one such species that was imported into quarantined laboratory conditions from Florida, USA. Host specificity trials were conducted using the same test plants as described for the studies on B. longulus, in addition to multigeneration trials to determine how long M. toddi could survive on non-target host plants. As with the B. longulus studies, no statistically significant differences in preference were observed between N. mexicana and N. nouchali, but M. toddi could not complete development on the test hybrid, indicating that this species is also unsuitable for the management of Nymphaea hybrids. Despite suboptimal plant health, M. toddi completed development for three generations on the native N. nouchali. This lack of host specificity deems M. toddi unsafe for release in South Africa but highlights the importance of following predefined steps to develop a biological control programme. The concluding chapter of this thesis discusses the aforementioned findings in a broader context by considering the driving forces of plant invasions in general and specifically for N. mexicana in South Africa. Case studies are also consulted to provide insight into how to proceed with managing Nymphaea hybrids in South Africa, while the factors governing host specificity and host range expansion are also discussed and considered in the context of B. longulus and M. toddi. Finally, after a consideration of the limitations of these studies, recommendations are made to continue the development of biological control for N. mexicana in South Africa. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-03-31
- Authors: Reid, Megan Kim
- Date: 2023-03-31
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/422554 , vital:71957 , DOI 10.21504/10962/422554
- Description: Nymphaea mexicana Zuccarini (Nymphaeaceae) is an invasive plant originating from southern USA and Mexico that has become problematic in South Africa, invading several water bodies around the country. Manual removal of this plant is very labour intensive and is not cost efficient or effective for long term control, while the use of herbicides is damaging to the environment and expensive. Consequently, this plant is a desirable candidate for biological control, which takes advantage of enemy release of the target weed and aims to re-establish population suppression induced by host specific natural enemies. Initiating biological control requires that several steps are followed to maximise the success of the programme, and the first few of these, including overseas surveys in the native range of the plant, have already been completed. This thesis aimed to continue biological control research for this species to take further steps at effectively managing the plant. Firstly, pre-release surveys in the invaded range are necessary to: determine what factors (including enemy release) contribute to the invasiveness of the target weed; establish a baseline of information to allow for comparison after biological control agents have been released; and identify any insect herbivores that may already be present in the country. The pre-release surveys conducted in this study revealed useful information about N. mexicana invasions in South Africa and provided evidence that enemy release is applicable to this case. However, these studies determined that a native weevil, Bagous longulus Gyllenhal (Coleoptera: Curculionidae), has expanded its host range to include the exotic N. mexicana at three sites, and may thus have potential for management of the species through augmentative releases. The invasion of N. mexicana in South Africa is further complicated by the presence of several Nymphaea hybrids originating from a complex history of horticultural trade. Although previous research has shown that several hybrid groups are present in South Africa, their parentage is not known. As biological control requires the use of host specific insects adapted to overcome the unique chemical and morphological defences utilised by plant species, hybrids are notoriously difficult to manage because they possess intermediate characters inherited from parent species to which natural enemies may not have adapted. Although biological control of hybrids is challenging, other case studies have demonstrated that it is possible to find suitable agents, but the chances of success are increased if putative parents of the hybrids are known so that they can be surveyed for natural enemies. Further molecular studies including possible parents of the Nymphaea hybrids in South Africa were thus carried out in this thesis to focus future surveying efforts. Two main hybrid groups were identified with genetic similarity to two tested putative Nymphaea parents, and this will allow further investigations of these species to improve the chances of successfully managing these hybrid groups. Some of the tested hybrids showed genetic contributions from multiple groups, some of which were unidentified, so it is necessary to prioritise the most problematic hybrids for biological control. With more insight into the genetic makeup of the Nymphaea hybrids in South Africa, investigations into the host specificity of potential biological control agents can be conducted. The ideal biological control agent should have a broad enough host range to impact and survive on both N. mexicana and its hybrids, but without a host range so broad that it would pose risk to native South African species. Host specificity trials are thus necessary to determine the suitability of potential agents. The identification of B. longulus feeding on N. mexicana during pre-release surveys motivated further investigations to determine the natural distribution, field host range, and host specificity of B. longulus in experimentally controlled conditions. Further surveys were therefore conducted at native Nymphaea sites around South Africa in addition to host specificity trials using the native Nymphaea nouchali Burm. f. (Nymphaeaceae), two populations of N. mexicana, and a cultivated hybrid. Results from the surveys and host specificity tests suggest that B. longulus is widely distributed across South Africa, is specific to Nymphaea with no observed preference between N. mexicana and the native N. nouchali, and does not perform well on Nymphaea hybrids. Hence, B. longulus is promising for use in new association biological control through augmentative releases but is not suitable for management of hybrids. In addition to the potential use of the South African B. longulus, it is necessary to conduct host specificity trials for natural enemies from the native range of N. mexicana that were prioritised in previous studies. Megamelus toddi Beamer (Hemiptera: Delphacidae) is one such species that was imported into quarantined laboratory conditions from Florida, USA. Host specificity trials were conducted using the same test plants as described for the studies on B. longulus, in addition to multigeneration trials to determine how long M. toddi could survive on non-target host plants. As with the B. longulus studies, no statistically significant differences in preference were observed between N. mexicana and N. nouchali, but M. toddi could not complete development on the test hybrid, indicating that this species is also unsuitable for the management of Nymphaea hybrids. Despite suboptimal plant health, M. toddi completed development for three generations on the native N. nouchali. This lack of host specificity deems M. toddi unsafe for release in South Africa but highlights the importance of following predefined steps to develop a biological control programme. The concluding chapter of this thesis discusses the aforementioned findings in a broader context by considering the driving forces of plant invasions in general and specifically for N. mexicana in South Africa. Case studies are also consulted to provide insight into how to proceed with managing Nymphaea hybrids in South Africa, while the factors governing host specificity and host range expansion are also discussed and considered in the context of B. longulus and M. toddi. Finally, after a consideration of the limitations of these studies, recommendations are made to continue the development of biological control for N. mexicana in South Africa. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-03-31
Assessing the density and distribution of spotted hyaenas (Crocuta crocuta) in Hluhluwe–iMfolozi Park, KwaZulu-Natal, South Africa
- Authors: Roberts, Peter Jean
- Date: 2022-04-06
- Subjects: Spotted hyena Home range South Africa Hluhluwe Game Reserve , Spotted hyena Habitat South Africa Hluhluwe Game Reserve , Animal population density South Africa Hluhluwe Game Reserve , Scouting cameras , Home range (Animal geography) , Spatially-explicit mark recapture (SECR)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/292681 , vital:57006
- Description: Protected areas are becoming increasingly isolated refugia for large carnivores and are critical for their survival. Spotted hyaenas (Crocuta crocuta) have, for centuries, been ‘managed’ as problem causing animals and their conservation has been largely overlooked. To preserve a population, it is paramount to understand its distribution and abundance through reliable and cost-effective monitoring techniques. My study estimated the density of spotted hyaenas and their use of space in Hluhluwe–iMfolozi Park (HiP), South Africa. I compared camera trap by-catch data and call-up surveys between 2013–2018 to assess spotted hyaena densities. The camera trap data estimated an average of 16.72 (SD: ±2.22) hyaenas per 100 km2 between 2013–2018, with an annual estimated high of 19.01 in 2018 and a low of 12.77 in 2015. The call-up surveys consistently produced lower estimates than those obtained from the camera trap data. These results highlight the importance of calibrating the response probability factor for call-up surveys to maintain precision. The space use of spotted hyaenas was analysed using the photo-capture data obtained during the same six-year period, to produce individual 100% Minimum Convex Polygon’s (MCPs). Seven clan territories were identified from individual female home ranges that overlapped by more than 66% of their MCPs. Territory sizes were similar to historical estimates for the park, with averages of 13.96 (SD: ±6.48) km2 in Hluhluwe and 34.61 (SD: ±23.87) km2 in iMfolozi. My study successfully used by-catch camera data to calculate annual density estimates and investigate the spatial use patterns for spotted hyaenas in HiP. I demonstrate that this approach is cost-effective and reliable for calculating density estimates. Conservation practitioners should take heed of the advancements in technology and analytical capacity now available to them to improve monitoring efforts. My study specifically calls for collaborative efforts to use existing camera trap data to improve regional estimates and population trends of spotted hyaenas across their range. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-04-06
- Authors: Roberts, Peter Jean
- Date: 2022-04-06
- Subjects: Spotted hyena Home range South Africa Hluhluwe Game Reserve , Spotted hyena Habitat South Africa Hluhluwe Game Reserve , Animal population density South Africa Hluhluwe Game Reserve , Scouting cameras , Home range (Animal geography) , Spatially-explicit mark recapture (SECR)
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/292681 , vital:57006
- Description: Protected areas are becoming increasingly isolated refugia for large carnivores and are critical for their survival. Spotted hyaenas (Crocuta crocuta) have, for centuries, been ‘managed’ as problem causing animals and their conservation has been largely overlooked. To preserve a population, it is paramount to understand its distribution and abundance through reliable and cost-effective monitoring techniques. My study estimated the density of spotted hyaenas and their use of space in Hluhluwe–iMfolozi Park (HiP), South Africa. I compared camera trap by-catch data and call-up surveys between 2013–2018 to assess spotted hyaena densities. The camera trap data estimated an average of 16.72 (SD: ±2.22) hyaenas per 100 km2 between 2013–2018, with an annual estimated high of 19.01 in 2018 and a low of 12.77 in 2015. The call-up surveys consistently produced lower estimates than those obtained from the camera trap data. These results highlight the importance of calibrating the response probability factor for call-up surveys to maintain precision. The space use of spotted hyaenas was analysed using the photo-capture data obtained during the same six-year period, to produce individual 100% Minimum Convex Polygon’s (MCPs). Seven clan territories were identified from individual female home ranges that overlapped by more than 66% of their MCPs. Territory sizes were similar to historical estimates for the park, with averages of 13.96 (SD: ±6.48) km2 in Hluhluwe and 34.61 (SD: ±23.87) km2 in iMfolozi. My study successfully used by-catch camera data to calculate annual density estimates and investigate the spatial use patterns for spotted hyaenas in HiP. I demonstrate that this approach is cost-effective and reliable for calculating density estimates. Conservation practitioners should take heed of the advancements in technology and analytical capacity now available to them to improve monitoring efforts. My study specifically calls for collaborative efforts to use existing camera trap data to improve regional estimates and population trends of spotted hyaenas across their range. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-04-06
Composition and physiological roles of gut microbiota in the False Coding Moth (Thaumatotibia leucotreta)
- Authors: Richardson, Perryn Heather
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424457 , vital:72155
- Description: Gut microbiota can have a profound influence on host performance, behaviour and fitness. For False Codling Moth (FCM), Thaumatotibia leucotreta (Lepidoptera: Tortricidae), a major pest of citrus in South Africa, little work has been undertaken to date on gut microbe diversity or its influence on the host. This thesis aimed to i) characterise the gut microbiome of FCM under laboratory conditions and in FCM from the field, ii) and produce moths with reduced gut microbiota through egg dechorionation, which was followed by iii) the measurement of a suite of physiological traits, namely mass, survival and thermal stress in FCM from normal laboratory, dechorionated laboratory and field collected larvae that may be indicative of overall field performance. We aimed to directly test the hypothesis that gut microbial diversity partly determines insect performance and fitness by measuring its effects on growth, development, and tolerance to cold temperatures in FCM. FCM eggs that underwent dechorionation with sodium hypochlorite had an overall effect on larval survival, egg morphology and both larval and adult moth physiological measures. Increasing concentrations of sodium hypochlorite significantly decreased insect survival, (𝜒2(1, n = 10 850) = 21.724, p-value < 0.0001), with a concentration of ≈3.69% as the concentration limit (p-value < 0.001). Successful dechorionation of FCM was achieved with a wash of sodium hypochlorite at around 3.69% concentration and was visually confirmed by reduction of FCM egg surface area, (𝜒2(25, n = 260) p-value < 0.0001) and Scanning Electron Micrographs of the egg morphology. The gut microbiome of FCM from the different focus treatments was successfully characterized. Identification of the dominant bacterial families in these microbiomes revealed Xanthobacteraceae, Beijerinckiaceae and Burkholderiaceae in both the laboratory reared and field collected larvae, which suggests their systematic association with T. leucotreta. The most abundant genera were revealed as Bradyrhizobium, Methylobacterium and Burkholderia-Caballeronia-Paraburkholderia. Comparison of larval mass showed that treatment (dechorionated or not) had a significant effect on larval mass (𝜒2(2, n = 230) = 22.703, p-value < 0.001), field larvae were heavier than both control larvae and larvae with a disrupted gut microbiome. However, adult insects with a disrupted gut microbiome had more mass than individuals from the control and field-collected larvae with intact gut microbiomes (𝜒2(2, n = 230) = 39.074, p-value < 0.001). Despite the difference in mass between larval treatments, there was no significant difference in relative protein (𝜒2(2, n = 24) = 5.680, p-value = 0.06), carbohydrate (𝜒2(2, n = 24) = 3.940, p-value = 0.14) or lipid (𝜒2(2, n = 24) = 6.032, p-value = 0.05) content between individuals from the control and dechorionated treatments and field-collected individuals. Turning to thermal physiology, insects collected from the field took significantly longer to recover from chill coma than both laboratory treatments with intact and disrupted gut microbiomes (𝜒2(2, n = 129 = 39.659, p-value < 0.001). In addition, exposure to cold stress showed that treatment had a significant effect on insect mortality (𝜒2(2, n = 272) = 9.176, p-value = 0.01), with individuals from the control and dechorionated treatment being less likely to die after experiencing cold stress compared to field-collected individuals. Differences in the mass and thermal tolerance of insects with intact and disrupted gut microbiota suggest that gut microbiota may play an important role in the cold performance of T. leucotreta, and these findings constitute the basis for future molecular work on the functions of these bacterial taxa. This research highlights the need for consideration of the effects of T. leucotreta microbiome in current pest control programs. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
- Authors: Richardson, Perryn Heather
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424457 , vital:72155
- Description: Gut microbiota can have a profound influence on host performance, behaviour and fitness. For False Codling Moth (FCM), Thaumatotibia leucotreta (Lepidoptera: Tortricidae), a major pest of citrus in South Africa, little work has been undertaken to date on gut microbe diversity or its influence on the host. This thesis aimed to i) characterise the gut microbiome of FCM under laboratory conditions and in FCM from the field, ii) and produce moths with reduced gut microbiota through egg dechorionation, which was followed by iii) the measurement of a suite of physiological traits, namely mass, survival and thermal stress in FCM from normal laboratory, dechorionated laboratory and field collected larvae that may be indicative of overall field performance. We aimed to directly test the hypothesis that gut microbial diversity partly determines insect performance and fitness by measuring its effects on growth, development, and tolerance to cold temperatures in FCM. FCM eggs that underwent dechorionation with sodium hypochlorite had an overall effect on larval survival, egg morphology and both larval and adult moth physiological measures. Increasing concentrations of sodium hypochlorite significantly decreased insect survival, (𝜒2(1, n = 10 850) = 21.724, p-value < 0.0001), with a concentration of ≈3.69% as the concentration limit (p-value < 0.001). Successful dechorionation of FCM was achieved with a wash of sodium hypochlorite at around 3.69% concentration and was visually confirmed by reduction of FCM egg surface area, (𝜒2(25, n = 260) p-value < 0.0001) and Scanning Electron Micrographs of the egg morphology. The gut microbiome of FCM from the different focus treatments was successfully characterized. Identification of the dominant bacterial families in these microbiomes revealed Xanthobacteraceae, Beijerinckiaceae and Burkholderiaceae in both the laboratory reared and field collected larvae, which suggests their systematic association with T. leucotreta. The most abundant genera were revealed as Bradyrhizobium, Methylobacterium and Burkholderia-Caballeronia-Paraburkholderia. Comparison of larval mass showed that treatment (dechorionated or not) had a significant effect on larval mass (𝜒2(2, n = 230) = 22.703, p-value < 0.001), field larvae were heavier than both control larvae and larvae with a disrupted gut microbiome. However, adult insects with a disrupted gut microbiome had more mass than individuals from the control and field-collected larvae with intact gut microbiomes (𝜒2(2, n = 230) = 39.074, p-value < 0.001). Despite the difference in mass between larval treatments, there was no significant difference in relative protein (𝜒2(2, n = 24) = 5.680, p-value = 0.06), carbohydrate (𝜒2(2, n = 24) = 3.940, p-value = 0.14) or lipid (𝜒2(2, n = 24) = 6.032, p-value = 0.05) content between individuals from the control and dechorionated treatments and field-collected individuals. Turning to thermal physiology, insects collected from the field took significantly longer to recover from chill coma than both laboratory treatments with intact and disrupted gut microbiomes (𝜒2(2, n = 129 = 39.659, p-value < 0.001). In addition, exposure to cold stress showed that treatment had a significant effect on insect mortality (𝜒2(2, n = 272) = 9.176, p-value = 0.01), with individuals from the control and dechorionated treatment being less likely to die after experiencing cold stress compared to field-collected individuals. Differences in the mass and thermal tolerance of insects with intact and disrupted gut microbiota suggest that gut microbiota may play an important role in the cold performance of T. leucotreta, and these findings constitute the basis for future molecular work on the functions of these bacterial taxa. This research highlights the need for consideration of the effects of T. leucotreta microbiome in current pest control programs. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
Disentangling the role of prokaryotes in regulating export flux via suspended and sinking organic matter in the southern ocean
- Authors: Dithugoe, Choaro David
- Date: 2022-10-14
- Subjects: Microbial ecology , Bioinformatics , Biochemistry , Oceanography , Metagenomics , Carbon cycle (Biogeochemistry) , Prokaryotes
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365745 , vital:65782 , DOI https://doi.org/10.21504/10962/365745
- Description: The role of phytoplankton in regulating atmospheric carbon dioxide in the marine environment has been the subject of extensive research. We lack, however, comparative insights regarding the functional contributions of bacteria, archaea, fungi, and viruses (the microbiota) to organic matter export especially in understudied polar marine environments such as the Southern Ocean. This knowledge deficit is in part due to the high levels of microbial diversity which obscures efforts to study the relationship between diversity and ecosystem functions including their roles in the sequestration of carbon and nitrogen. Elucidating their precise contributions to organic matter export may be central to potential ecosystems feedbacks to global climate change. We examined several factors which may influence organic matter export to depth including net primary production, phytoplankton biomass, temperature, and prokaryotic functional capacity in the Southern Ocean. A Marine Snow Catcher was used to collect suspended and sinking material 10 metres below mixed layer depth at Southern Ocean Time Series (SOTS) in autumn (March-April) and in the Atlantic sector of the Southern Ocean in winter (July-August) and spring (October-November) 2019. The suspended and sinking material was used to determine the particulate organic carbon and nitrogen concentrations which were then used to calculate fluxes and export ratio ((e-ratio) - particulate organic carbon flux divided by net primary production). Additionally, genomic DNA was extracted from the suspended and sinking material and sequenced to obtain Shotgun metagenomic data which was employed to reconstruct metagenome assembled genome (MAGs) and their functional capacity using bioinformatic tools such as DRAM. Data from the Atlantic sector of the Southern Ocean, demonstrate that net primary production and temperature were inversely related to the e-ratio which is consistent with previous findings from the northern region of the Southern Ocean. Genomic functional capacity from SOTS suggested that r-strategist (organisms adapted to live in unstable environments) bacteria (e.g., Gammaproteobacteria) were prominent in the suspended pool. By contrast, the sinking particle-pool appeared to be dominated by K- strategists (organisms adapted to stable environment). The opposite was true for the archaea. This finding (i.e., bacteria) differs from a previous study in the northern region of the Southern Ocean, showing that microbes with K-strategists were more abundant in the suspended fraction. K-strategists typically degrade sinking organic matter into suspended organic matter or dissolved organic matter reducing the organic carbon export efficiency. Furthermore, Data from the Atlantic sector of the Southern Ocean revealed that seasonal temperature changes might dictate the rate of regional prokaryotic degradation across the zones. Resulting in rapid degradation at the northerly warmer regions and slow degradation further south. The data further provide evidence of chemolithoautotrophic mechanisms, with prokaryotes harbouring key pathways, required to transform dissolved inorganic carbon into complex organic forms, including recalcitrant dissolved organic carbon. Collectively, the SOTS and Atlantic sector of the Southern Ocean data suggest that shifts in prokaryotic community structure and functional capacity may regulate (either degradation or synthesis of organic matter) carbon export to depth. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Dithugoe, Choaro David
- Date: 2022-10-14
- Subjects: Microbial ecology , Bioinformatics , Biochemistry , Oceanography , Metagenomics , Carbon cycle (Biogeochemistry) , Prokaryotes
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365745 , vital:65782 , DOI https://doi.org/10.21504/10962/365745
- Description: The role of phytoplankton in regulating atmospheric carbon dioxide in the marine environment has been the subject of extensive research. We lack, however, comparative insights regarding the functional contributions of bacteria, archaea, fungi, and viruses (the microbiota) to organic matter export especially in understudied polar marine environments such as the Southern Ocean. This knowledge deficit is in part due to the high levels of microbial diversity which obscures efforts to study the relationship between diversity and ecosystem functions including their roles in the sequestration of carbon and nitrogen. Elucidating their precise contributions to organic matter export may be central to potential ecosystems feedbacks to global climate change. We examined several factors which may influence organic matter export to depth including net primary production, phytoplankton biomass, temperature, and prokaryotic functional capacity in the Southern Ocean. A Marine Snow Catcher was used to collect suspended and sinking material 10 metres below mixed layer depth at Southern Ocean Time Series (SOTS) in autumn (March-April) and in the Atlantic sector of the Southern Ocean in winter (July-August) and spring (October-November) 2019. The suspended and sinking material was used to determine the particulate organic carbon and nitrogen concentrations which were then used to calculate fluxes and export ratio ((e-ratio) - particulate organic carbon flux divided by net primary production). Additionally, genomic DNA was extracted from the suspended and sinking material and sequenced to obtain Shotgun metagenomic data which was employed to reconstruct metagenome assembled genome (MAGs) and their functional capacity using bioinformatic tools such as DRAM. Data from the Atlantic sector of the Southern Ocean, demonstrate that net primary production and temperature were inversely related to the e-ratio which is consistent with previous findings from the northern region of the Southern Ocean. Genomic functional capacity from SOTS suggested that r-strategist (organisms adapted to live in unstable environments) bacteria (e.g., Gammaproteobacteria) were prominent in the suspended pool. By contrast, the sinking particle-pool appeared to be dominated by K- strategists (organisms adapted to stable environment). The opposite was true for the archaea. This finding (i.e., bacteria) differs from a previous study in the northern region of the Southern Ocean, showing that microbes with K-strategists were more abundant in the suspended fraction. K-strategists typically degrade sinking organic matter into suspended organic matter or dissolved organic matter reducing the organic carbon export efficiency. Furthermore, Data from the Atlantic sector of the Southern Ocean revealed that seasonal temperature changes might dictate the rate of regional prokaryotic degradation across the zones. Resulting in rapid degradation at the northerly warmer regions and slow degradation further south. The data further provide evidence of chemolithoautotrophic mechanisms, with prokaryotes harbouring key pathways, required to transform dissolved inorganic carbon into complex organic forms, including recalcitrant dissolved organic carbon. Collectively, the SOTS and Atlantic sector of the Southern Ocean data suggest that shifts in prokaryotic community structure and functional capacity may regulate (either degradation or synthesis of organic matter) carbon export to depth. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
Distribution and habitat preferences of marine megafauna in Nosy Be, Madagascar
- Authors: Lubbé, Alicea
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424710 , vital:72177
- Description: Marine megafauna have important ecological roles including the top-down regulation of lower trophic levels and the transport of nutrients. They are also charismatic species of socioeconomic importance, due to their public appeal and focus for ecotourism. However, these taxa face numerous anthropogenic threats including bycatch, habitat-loss, noise disturbance, prey reductions, pollution, and vessel traffic. Northwest Madagascar has been identified as an important marine mammal area and whale shark aggregation site, yet limited information on megafauna within Madagascar exists. In this thesis, I investigated the community structure, distribution trends, related environmental factors (Chapter 2) and predicted habitat suitability (Chapter 3) using a species distribution modelling approach for marine megafauna around Nosy Be, North-west Madagascar. Data collection consisted of opportunistic boatbased surveys conducted while looking for whale sharks, mobulid rays and cetaceans. These activities were performed by dedicated ‘swim with whale shark’ tourism operators, Les Baleines Rand'eau and Safari Baleine during tourism activities directed by the Madagascar Whale Shark Project over four years (2016-2019). A total of 1792 sightings were reported with 13 identified species, including elasmobranchs: whale shark, Rhincodon typus; spinetail mobula ray, Mobula japonica; giant oceanic manta ray, Manta birostris; shortfin devil ray, Mobula kuhlii; balaenids: humpback whale, Megaptera novaeangliae; Omura's whale, Balaenoptera omurai, delphinids: Indo-Pacific bottlenose dolphin, Tursiops aduncus; spinner dolphin, Stenella longirostris; pantropical spotted dolphin, Stenella attenuata; Indian ocean humpback dolphin, Sousa plumbea; false killer whale, Pseudorca crassidens; melonheaded whale, Peponocephala electra and one cheloniid species: leatherback sea turtle, Dermochelys coriacea. Sightings were spatially analysed at a community level according to feeding guilds (i.e., filter feeders vs. predators), and distribution of the megafauna groups v were compared to selected remotely sensed physico-chemical data (sea surface temperature and chlorophyll-a concentration) and bathymetry charts (depth and slope) using generalized linear models (Chapter 2). All four variables had a significant effect on filter feeder distribution. Spatial distribution of filter feeder sightings peaked at an area of steep underwater topography (18-50m; x slope=0.5%) located on the west coast of Nosy Be, where foraging aggregations of large filter feeders (primarily R. typus and B. omurai) were frequently observed. Only SST had a significant effect on the relative abundance of animals in the predator feeding guild, which demonstrated a more longitudinal distribution along the continental shelf. The maximum entropy model (Maxent) was used for predicting habitat preference for the most frequently sighted species (Chapter 3). The distribution of whale sharks, mobulid rays and Omura’s whales were significantly overlapped as they were abundant in two main hotspots, Grand banc de l’entrée (~10 km of the west coast) and near Nosy Mitsio island, (~50 km northeast of Nosy Be). Suitable habitat for the dolphins was in relatively shallow waters in temperatures <28ºC near areas of steep changes in bathymetry. Bottlenose and spinner dolphins had a more widespread distribution across the continental shelf and humpback dolphin was closely associated with inshore reefs and occur in waters <10m. The coastal and inshore region of Nosy Be is an important habitat for a variety of megafaunal species, and the continental shelf provided essential areas for feeding and breeding. The results were similar to those presented for these species in other regions of the Indian Ocean (i.e., Eastern and Southern Africa; Western Australia; Seychelles) as well as outside of the Indian Ocean (i.e., Indonesia; Caribbean; North Atlantic). Thus the results from this thesis could be considered for management recommendations for marine conservation in the region. The value and limitations of data collected by citizen science were outlined (Chapter 4). , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
- Authors: Lubbé, Alicea
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424710 , vital:72177
- Description: Marine megafauna have important ecological roles including the top-down regulation of lower trophic levels and the transport of nutrients. They are also charismatic species of socioeconomic importance, due to their public appeal and focus for ecotourism. However, these taxa face numerous anthropogenic threats including bycatch, habitat-loss, noise disturbance, prey reductions, pollution, and vessel traffic. Northwest Madagascar has been identified as an important marine mammal area and whale shark aggregation site, yet limited information on megafauna within Madagascar exists. In this thesis, I investigated the community structure, distribution trends, related environmental factors (Chapter 2) and predicted habitat suitability (Chapter 3) using a species distribution modelling approach for marine megafauna around Nosy Be, North-west Madagascar. Data collection consisted of opportunistic boatbased surveys conducted while looking for whale sharks, mobulid rays and cetaceans. These activities were performed by dedicated ‘swim with whale shark’ tourism operators, Les Baleines Rand'eau and Safari Baleine during tourism activities directed by the Madagascar Whale Shark Project over four years (2016-2019). A total of 1792 sightings were reported with 13 identified species, including elasmobranchs: whale shark, Rhincodon typus; spinetail mobula ray, Mobula japonica; giant oceanic manta ray, Manta birostris; shortfin devil ray, Mobula kuhlii; balaenids: humpback whale, Megaptera novaeangliae; Omura's whale, Balaenoptera omurai, delphinids: Indo-Pacific bottlenose dolphin, Tursiops aduncus; spinner dolphin, Stenella longirostris; pantropical spotted dolphin, Stenella attenuata; Indian ocean humpback dolphin, Sousa plumbea; false killer whale, Pseudorca crassidens; melonheaded whale, Peponocephala electra and one cheloniid species: leatherback sea turtle, Dermochelys coriacea. Sightings were spatially analysed at a community level according to feeding guilds (i.e., filter feeders vs. predators), and distribution of the megafauna groups v were compared to selected remotely sensed physico-chemical data (sea surface temperature and chlorophyll-a concentration) and bathymetry charts (depth and slope) using generalized linear models (Chapter 2). All four variables had a significant effect on filter feeder distribution. Spatial distribution of filter feeder sightings peaked at an area of steep underwater topography (18-50m; x slope=0.5%) located on the west coast of Nosy Be, where foraging aggregations of large filter feeders (primarily R. typus and B. omurai) were frequently observed. Only SST had a significant effect on the relative abundance of animals in the predator feeding guild, which demonstrated a more longitudinal distribution along the continental shelf. The maximum entropy model (Maxent) was used for predicting habitat preference for the most frequently sighted species (Chapter 3). The distribution of whale sharks, mobulid rays and Omura’s whales were significantly overlapped as they were abundant in two main hotspots, Grand banc de l’entrée (~10 km of the west coast) and near Nosy Mitsio island, (~50 km northeast of Nosy Be). Suitable habitat for the dolphins was in relatively shallow waters in temperatures <28ºC near areas of steep changes in bathymetry. Bottlenose and spinner dolphins had a more widespread distribution across the continental shelf and humpback dolphin was closely associated with inshore reefs and occur in waters <10m. The coastal and inshore region of Nosy Be is an important habitat for a variety of megafaunal species, and the continental shelf provided essential areas for feeding and breeding. The results were similar to those presented for these species in other regions of the Indian Ocean (i.e., Eastern and Southern Africa; Western Australia; Seychelles) as well as outside of the Indian Ocean (i.e., Indonesia; Caribbean; North Atlantic). Thus the results from this thesis could be considered for management recommendations for marine conservation in the region. The value and limitations of data collected by citizen science were outlined (Chapter 4). , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
Effect of Helicosporidium sp. (Chlorophyta; Trebouxiophyceae) infection on Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae), a biological control agent for the invasive Salvinia molesta D.S. Mitchell (Salviniaceae) in South
- Authors: Mphephu, Tshililo Emmanuel
- Date: 2022-10-14
- Subjects: Salvinia molesta South Africa , Weeds Biological control , Cyrtobagous salviniae , Ketoconazole
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365815 , vital:65792 , DOI https://doi.org/10.21504/10962/365815
- Description: The effectiveness of established biological control agents depends on biotic and abiotic interactions in the introduced range. The weevil, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae), was released as a biological control against Salvinia molesta D.S. Mitchell (Salviniaceae) in South Africa in 1985. This agent has been highly successful against S. molesta and has significantly reduced the weed’s populations around the country. However, in 2007, the parasitic alga, Helicosporidium sp. (an undescribed species), was detected in field-collected C. salviniae adults in South Africa. The distribution and impacts of this disease on the weevil and its efficacy as a control agent were not known. In this thesis, the prevalence, infection load, and impact of Helicosporidium sp. on C. salviniae was determined. In 2019, adult weevils were collected from 10 sites across the Eastern Cape, KwaZulu-Natal, Limpopo, and Western Cape provinces and screened to determine the occurrence, infection load, and geographic distribution of Helicosporidium sp. Transmission mechanisms of this disease in C. salviniae were then evaluated. The possible impact of Helicosporidium sp. was assessed by comparing the feeding rates and the reproductive output of the diseased and healthy adults of C. salviniae. An attempt was then made to eliminate the disease in C. salviniae through the application of the antibiotic, ketoconazole. Further, the role of temperature on infection load in C. salviniae was also assessed. Finally, recommendations for the long-term biological control programme against S. molesta in South Africa were made. The disease covers the entire distribution range of C. salviniae in South Africa, with the disease occurrence rate ranging from 92.15% to 100% insects infected per site. Helicosporidium sp. was found to transmit vertically within the populations of C. salviniae. Infection by the Helicosporidium sp. disease reduced the reproductive output of C. salviniae as well its impact on biomass reduction of S. molesta when a diseased culture was compared to a healthy culture from the USA. 98.44 to 98.55% of Helicosporidium sp. loads were reduced through multiple applications of ketoconazole concentrations under in vitro trials. In vivo treatments resulted in 70% control of Helicosporidium sp. in the adults of C. salviniae that were fed ketoconazole three times over a 21 day period. Adult C. salviniae feeding and survival performances were similar when fed fronds of S. molesta inoculated with ketoconazole and water. The lowest and highest disease loads of Helicosporidium sp. were recorded when the weevils were reared at 30°C and 14°C, respectively. As expected, the highest impact and reproductive output of C. salviniae were at 30°C. The evaluations discussed in this thesis highlight the role of diseases in biological control agents, and gaps in both the pre-release and post-release monitoring that should integrate screening of diseases in these studies. Although the combined application of the antibiotic and temperature will reduce Helicosporidium sp. loads and impact, this technology is most likely only applicable where the weevils are reared in small numbers in a rearing facility and not really applicable to the field situation. It is important to release healthy agents that will cause efficient control of the target weed plant species, therefore, when introducing new biological control agents, the health status of such agents needs to be understood. Therefore, long-term field monitoring and assessment of the impact of C. salviniae on S. molesta should be conducted to track all the changes that may result due to the presence of Helicosporidium sp. This long-term monitoring and assessment will give a more informative role of Helicosporidium sp. in field populations of C. salviniae. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Mphephu, Tshililo Emmanuel
- Date: 2022-10-14
- Subjects: Salvinia molesta South Africa , Weeds Biological control , Cyrtobagous salviniae , Ketoconazole
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365815 , vital:65792 , DOI https://doi.org/10.21504/10962/365815
- Description: The effectiveness of established biological control agents depends on biotic and abiotic interactions in the introduced range. The weevil, Cyrtobagous salviniae Calder and Sands (Coleoptera: Curculionidae), was released as a biological control against Salvinia molesta D.S. Mitchell (Salviniaceae) in South Africa in 1985. This agent has been highly successful against S. molesta and has significantly reduced the weed’s populations around the country. However, in 2007, the parasitic alga, Helicosporidium sp. (an undescribed species), was detected in field-collected C. salviniae adults in South Africa. The distribution and impacts of this disease on the weevil and its efficacy as a control agent were not known. In this thesis, the prevalence, infection load, and impact of Helicosporidium sp. on C. salviniae was determined. In 2019, adult weevils were collected from 10 sites across the Eastern Cape, KwaZulu-Natal, Limpopo, and Western Cape provinces and screened to determine the occurrence, infection load, and geographic distribution of Helicosporidium sp. Transmission mechanisms of this disease in C. salviniae were then evaluated. The possible impact of Helicosporidium sp. was assessed by comparing the feeding rates and the reproductive output of the diseased and healthy adults of C. salviniae. An attempt was then made to eliminate the disease in C. salviniae through the application of the antibiotic, ketoconazole. Further, the role of temperature on infection load in C. salviniae was also assessed. Finally, recommendations for the long-term biological control programme against S. molesta in South Africa were made. The disease covers the entire distribution range of C. salviniae in South Africa, with the disease occurrence rate ranging from 92.15% to 100% insects infected per site. Helicosporidium sp. was found to transmit vertically within the populations of C. salviniae. Infection by the Helicosporidium sp. disease reduced the reproductive output of C. salviniae as well its impact on biomass reduction of S. molesta when a diseased culture was compared to a healthy culture from the USA. 98.44 to 98.55% of Helicosporidium sp. loads were reduced through multiple applications of ketoconazole concentrations under in vitro trials. In vivo treatments resulted in 70% control of Helicosporidium sp. in the adults of C. salviniae that were fed ketoconazole three times over a 21 day period. Adult C. salviniae feeding and survival performances were similar when fed fronds of S. molesta inoculated with ketoconazole and water. The lowest and highest disease loads of Helicosporidium sp. were recorded when the weevils were reared at 30°C and 14°C, respectively. As expected, the highest impact and reproductive output of C. salviniae were at 30°C. The evaluations discussed in this thesis highlight the role of diseases in biological control agents, and gaps in both the pre-release and post-release monitoring that should integrate screening of diseases in these studies. Although the combined application of the antibiotic and temperature will reduce Helicosporidium sp. loads and impact, this technology is most likely only applicable where the weevils are reared in small numbers in a rearing facility and not really applicable to the field situation. It is important to release healthy agents that will cause efficient control of the target weed plant species, therefore, when introducing new biological control agents, the health status of such agents needs to be understood. Therefore, long-term field monitoring and assessment of the impact of C. salviniae on S. molesta should be conducted to track all the changes that may result due to the presence of Helicosporidium sp. This long-term monitoring and assessment will give a more informative role of Helicosporidium sp. in field populations of C. salviniae. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
Enteric microbial responses to host hyperthermia in southern African insectivorous bats: a test of thermal co-adaptation
- Authors: Hunter, Amy Alison
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424391 , vital:72149
- Description: Embargoed. Expected release date 2025. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
- Authors: Hunter, Amy Alison
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424391 , vital:72149
- Description: Embargoed. Expected release date 2025. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
Evaluation of potential oviposition deterrents for false codling moth, Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae)
- Authors: Dambuza, Khalipha
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424479 , vital:72157
- Description: There has been extensive research on the use of semiochemicals as deterrents or true repellents in insect pest management, particularly in push-pull strategies. Much of this research has focused on pests of medical and veterinary importance and has been limited for agricultural pests. This means there is an opportunity to study use of deterrents to manage pests of agricultural importance. No study has been conducted on deterrents for false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), a key phytosanitary pest in citrus orchards across South Africa. This study assessed FCM oviposition deterrence in botanicals (plants (n = 11) and essential oils (n = 15)), and some commercial pesticides (n = 7) used for FCM control in South Africa. All tested botanicals were selected based on an extensive literature review of plant compounds that have been reported to deter or repel lepidopteran pests. Choice and no-choice oviposition bioassays were conducted in complete darkness in a controlled environment room. Oranges treated with solutions/suspensions of potential oviposition deterrents were placed into a cage with gravid FCM females for four hours, with oviposition being recorded every hour. Of the 33 tested compounds, only eight significantly reduced FCM oviposition (P < 0.05) compared to the control in oviposition bioassays i.e. two essential oils (lavender and peppermint), two plant crude extracts (garlic and marigold), one fruit (Mango), and three commercial FCM insecticides (Delegate, Coragen, and Warlock). All identified oviposition deterrents, except for Mango, were further investigated for their ovicidal properties in concentration response bioassays, where all botanicals were identified to have dual action (both deterrent and ovicidal properties), as they significantly (P < 0.05) reduced FCM oviposition and egg hatch. Garlic was the most efficacious botanical whilst Warlock was the only commercial insecticide that did not show ovicidal activity (F = 41.17, P = 0.0622). Larval penetration of the host fruit was less than egg hatch for all tested compounds in concentration response bioassays. Oviposition, egg hatch, and larval penetration were all affected by concentration, with the higher concentrations being the most effective. The efficacy of these deterrent compounds should be further tested in semi-field and/or field trials, and they may have potential in FCM management as allomone dispensers or sprays. They can also be implemented in push-pull strategies where they can be used in conjunction with FCM attractants. Lastly, repellence studies should be conducted in absentia of the host fruit to determine whether oviposition deterrence was a result of true repellence or odour masking. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
- Authors: Dambuza, Khalipha
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424479 , vital:72157
- Description: There has been extensive research on the use of semiochemicals as deterrents or true repellents in insect pest management, particularly in push-pull strategies. Much of this research has focused on pests of medical and veterinary importance and has been limited for agricultural pests. This means there is an opportunity to study use of deterrents to manage pests of agricultural importance. No study has been conducted on deterrents for false codling moth (FCM), Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), a key phytosanitary pest in citrus orchards across South Africa. This study assessed FCM oviposition deterrence in botanicals (plants (n = 11) and essential oils (n = 15)), and some commercial pesticides (n = 7) used for FCM control in South Africa. All tested botanicals were selected based on an extensive literature review of plant compounds that have been reported to deter or repel lepidopteran pests. Choice and no-choice oviposition bioassays were conducted in complete darkness in a controlled environment room. Oranges treated with solutions/suspensions of potential oviposition deterrents were placed into a cage with gravid FCM females for four hours, with oviposition being recorded every hour. Of the 33 tested compounds, only eight significantly reduced FCM oviposition (P < 0.05) compared to the control in oviposition bioassays i.e. two essential oils (lavender and peppermint), two plant crude extracts (garlic and marigold), one fruit (Mango), and three commercial FCM insecticides (Delegate, Coragen, and Warlock). All identified oviposition deterrents, except for Mango, were further investigated for their ovicidal properties in concentration response bioassays, where all botanicals were identified to have dual action (both deterrent and ovicidal properties), as they significantly (P < 0.05) reduced FCM oviposition and egg hatch. Garlic was the most efficacious botanical whilst Warlock was the only commercial insecticide that did not show ovicidal activity (F = 41.17, P = 0.0622). Larval penetration of the host fruit was less than egg hatch for all tested compounds in concentration response bioassays. Oviposition, egg hatch, and larval penetration were all affected by concentration, with the higher concentrations being the most effective. The efficacy of these deterrent compounds should be further tested in semi-field and/or field trials, and they may have potential in FCM management as allomone dispensers or sprays. They can also be implemented in push-pull strategies where they can be used in conjunction with FCM attractants. Lastly, repellence studies should be conducted in absentia of the host fruit to determine whether oviposition deterrence was a result of true repellence or odour masking. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
Freshwater invasive alien crayfish species in South Africa: testing eDNA assessment and DNA barcoding
- Mdidimba, Nonkazimulo Dorothea
- Authors: Mdidimba, Nonkazimulo Dorothea
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424413 , vital:72151
- Description: The expansion of the wild populations of the two invasive alien crayfish species, i.e., Cherax quadricarinatus and Procambarus clarkii in South Africa is of high concern. Given this, innovative and improved monitoring methods are required to be explored in order to effectively detect and manage their spread. Environmental DNA (eDNA) has shown promising and reliable results to detect and monitor alien crayfish in freshwater systems even at low densities. This research study aimed to field-test the application of eDNA for detecting and monitoring invasive alien freshwater crayfish species (IAFCs) in South African freshwater systems (Chapter 2). Further, this study also aimed to confirm the true taxonomic identity of the IAFCs in South African freshwater systems by using DNA barcoding to avoid potential misidentifications with morphological identification alone (Chapter 3). Also, ectocommensal temnocephalans and leeches attached to the crayfishes were also identified with DNA barcoding. The mitochondrial COI gene fragment of the crayfishes and the ectocommensal temnocephalans and leeches was amplified, sequenced, and used for species identification. For eDNA monitoring of C. cainii, C. quadricarinatus and P. clarkii, water samples were collected from Eastern Cape, Free State and KwaZulu Natal sites that are known to house these species. The current study did not detect the eDNA of the wild populations of both C. quadricarinatus and P. clarkii. This failure was encountered despite employing several methods, such as, end-point polymerase chain reaction (PCR), quantitative PCR (qPCR) and next-generation sequencing (NGS). The eDNA assessment to detect IAFCs in the wild populations is discussed in detail, and corrective measures suggested (Chapter 2). However, only C. cainii was able to be detected by eDNA. Cherax cainii is housed/farmed in an aquaculture facility (Vaughn Bursey’s Stock Farm in Eastern Cape) with large number of individuals per pond. For this, NGS was able to detect C. cainii but the other two methods, end-point PCR and qPCR were not able to detect the species. Based on the results, refinement of eDNA monitoring methods for the South African freshwater systems is recommended. Evaluation of different DNA collection methods, preservation, DNA extraction kits and primer design to obtain effective eDNA detection is discussed as possible sources of error. Interestingly, the newly established population of P. clarkii in Mimosa Dam in Free State was infested with alien leeches, that were confirmed by DNA barcoding to be Helobdella europaea and Helobdella octatestica. Consequently, this study reports for the first time in South Africa the presence of this alien freshwater leeches. The presence of alien leeches and P. clarkii suggests a double invasion in Mimosa Dam, P. clarkii seems to continue expanding its range in the country. However, the long-established population of P. clarkii in Driehoek Farm in Mpumalanga, which has been in the country for over 30 years did not have any leech or temnocephalan infestation. This could suggest several interesting ecological phenomena, including environmental filtering over time of the co-invaders, differential source populations, and post-introduction adaptation. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
- Authors: Mdidimba, Nonkazimulo Dorothea
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424413 , vital:72151
- Description: The expansion of the wild populations of the two invasive alien crayfish species, i.e., Cherax quadricarinatus and Procambarus clarkii in South Africa is of high concern. Given this, innovative and improved monitoring methods are required to be explored in order to effectively detect and manage their spread. Environmental DNA (eDNA) has shown promising and reliable results to detect and monitor alien crayfish in freshwater systems even at low densities. This research study aimed to field-test the application of eDNA for detecting and monitoring invasive alien freshwater crayfish species (IAFCs) in South African freshwater systems (Chapter 2). Further, this study also aimed to confirm the true taxonomic identity of the IAFCs in South African freshwater systems by using DNA barcoding to avoid potential misidentifications with morphological identification alone (Chapter 3). Also, ectocommensal temnocephalans and leeches attached to the crayfishes were also identified with DNA barcoding. The mitochondrial COI gene fragment of the crayfishes and the ectocommensal temnocephalans and leeches was amplified, sequenced, and used for species identification. For eDNA monitoring of C. cainii, C. quadricarinatus and P. clarkii, water samples were collected from Eastern Cape, Free State and KwaZulu Natal sites that are known to house these species. The current study did not detect the eDNA of the wild populations of both C. quadricarinatus and P. clarkii. This failure was encountered despite employing several methods, such as, end-point polymerase chain reaction (PCR), quantitative PCR (qPCR) and next-generation sequencing (NGS). The eDNA assessment to detect IAFCs in the wild populations is discussed in detail, and corrective measures suggested (Chapter 2). However, only C. cainii was able to be detected by eDNA. Cherax cainii is housed/farmed in an aquaculture facility (Vaughn Bursey’s Stock Farm in Eastern Cape) with large number of individuals per pond. For this, NGS was able to detect C. cainii but the other two methods, end-point PCR and qPCR were not able to detect the species. Based on the results, refinement of eDNA monitoring methods for the South African freshwater systems is recommended. Evaluation of different DNA collection methods, preservation, DNA extraction kits and primer design to obtain effective eDNA detection is discussed as possible sources of error. Interestingly, the newly established population of P. clarkii in Mimosa Dam in Free State was infested with alien leeches, that were confirmed by DNA barcoding to be Helobdella europaea and Helobdella octatestica. Consequently, this study reports for the first time in South Africa the presence of this alien freshwater leeches. The presence of alien leeches and P. clarkii suggests a double invasion in Mimosa Dam, P. clarkii seems to continue expanding its range in the country. However, the long-established population of P. clarkii in Driehoek Farm in Mpumalanga, which has been in the country for over 30 years did not have any leech or temnocephalan infestation. This could suggest several interesting ecological phenomena, including environmental filtering over time of the co-invaders, differential source populations, and post-introduction adaptation. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
Functional biogeography: evaluating community assemblage patterns and ecosystem functioning in intertidal systems using trait-based approaches
- Authors: Gusha, Molline Natanah C
- Date: 2022-10-14
- Subjects: Biogeography , Marine algae , Benthic ecology , Invertebrates , Functional redundancy , Ocean temperature , Biology Classification
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365792 , vital:65790 , DOI https://doi.org/10.21504/10962/365792
- Description: Analyses of taxonomic diversity patterns within coastal systems has been critical in the development of the theory of biogeography. Increasing evidence, however, shows that the variety of functions that species perform in ecosystems (rather than their taxonomic identity) is a better predictor of the influence of the environment on the species. This information has been useful in predictive ecology leading to the development of trait-based approaches (TBA). Until the late 1970s, however, limited effort (particularly in marine systems) was channeled towards patterns in functional species traits and how they may be affected by changes in environmental gradients. Here, I mapped the functional biogeography of the South African coastline based on a suite of species' reproduction and development traits. Because species composition is one of the key tools used by zoogeographers to map species distribution patterns, I expected lower variability in trait composition within main biogeographic regions than in intervening transition zones based on the habitat templet theory and following the biomass ratio and limiting similarity hypotheses. In brief, the habitat templet theory proposes that “the habitat provides a templet upon which evolution forges species characteristics”, while the biomass ratio hypothesis assumes that the most abundant species traits determine ecosystem functioning. The limiting similarity hypothesis also sometimes referred to as the niche complementarity hypothesis, however, predicts that species can coexist if their niches complement one another. In light of the habitat being an evolutionary templet, abiotic and biotic habitat patterns were measured as nearshore SST and chlorophyll-a gradients, respectively. I expected the SST gradient to act as the stronger key filter of trait diversification because temperature is often considered the most influential environmental factor affecting species survival with seasonality of SST affecting the timing of spawning and along with food availability, possibly influencing fecundity. Functional trait data were thus compiled for macroinvertebrate species collected from fifty-two rocky shore sites from three main bioregions (east, south, and west) and two transition zones (south-west and south-east). Biological trait analysis and functional diversity indices were used to evaluate how traits related to species development and reproduction respond to temperature and chlorophyll -a (used as a proxy for food availability) gradients along the coastline. GLMM and hierarchical cluster analyses showed distinct patterns/shifts in SST and chlorophyll-a gradients across bioregions, with two main breaks in SST separating the east and south-east overlap (SEO) bioregions from the south, south-west overlap (SWO) and west bioregions. In contrast, chlorophyll-a exhibited three major breaks with the east, SEO–south–SWO, and west clustering independently of each other. The RLQ analysis (a type of co-inertia analysis) which simultaneously ordinates 3-matrix datasets [i.e., (environment × site[R]), (species × site[L]) and (species × traits [Q])] showed that the higher SST gradient on the east and SEO promoted higher abundance and biomass of simultaneous hermaphrodites while higher chlorophyll-a gradients on the SWO and west coasts strongly promoted reproductive maturity at larger-sizes. The combined fourth-corner analyses showed that the modalities within the development trait domain responding to chlorophyll-a gradients primarily included filter feeders, sessile and swimming species and also species living on the infratidal zone. In addition, the reproduction trait domain showed higher sensitivity and association to differences in chlorophyll-a and SST gradients than development traits. Overall, SST and chlorophyll-a gradients influenced the distribution of the most dominant traits as indicated by shifts in community-weighted mean trait values across bioregions. This suggests the importance of habitat filtering on coastal species reproduction. A separate study evaluating the influence of large-scale biogeographic effects vs the micro-scale biogenic habitat structure offered by coralline seaweeds across 24 sites revealed some notable effects of both factors on the diversity and abundance of macroalgal epifauna. There was a notable biogeographic influence on epifauna, with the SEO recording the highest epifaunal species richness and abundance, followed by the south coast, then the SWO and lastly the west coast. In addition, the total biomass gradient of the corallines followed a similar trend. The epifauna however, showed no host-specificity, illustrating that epifauna may not be species–centric as commonly assumed, and the higher diversity of epifaunal diversity may well be simply because those corallines are the available habitat within the sampled part of the coastline. Lastly, macroinvertebrate trait distribution on the South African coastline confirms that the habitat, particularly the biotic filter (in this case chl-a) provides a templet upon which evolution forges species traits. However, since temperature is a proxy for nutrient availability (cold upwelling brings nutrients), then temperature drives chlorophyll-a. Subsequently this means the abiotic component indirectly drives trait distribution by influencing the biotic environment (chl-a). For epifauna species, also, the coralline diversity and composition can also be regarded as a biotic filter influencing the epifaunal abundances and composition across different bioregions. Moreover, since temperature is regarded as a conservative trait in seaweeds, temperature tolerance defines the biogeographical boundaries of seaweeds, therefore temperature may be indirectly affecting epifauna abundances through coralline species diversity and biomass. In summary, considering the deterministic processes governing ecosystem functioning and community assemblage, the mass ratio and limiting similarity hypotheses showed complementary effects. Different bioregions provided variable support for these two hypotheses, but overall, the mass ratio hypothesis (weighted by species biomass) received stronger support and may be more meaningful to the interpretation of ecosystem functioning and persistence within rocky shore systems. Lastly, although, the SWO showed some of the characteristics of a subtraction zone based on the relatively low abundance, diversity, and biomass measures. Nonetheless, there was evidence of high functional redundancy across all other four bioregions. This suggests that in the context of development and reproduction traits, the rocky shore ecosystem along the SA coastline may be functionally stable at this stage. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Gusha, Molline Natanah C
- Date: 2022-10-14
- Subjects: Biogeography , Marine algae , Benthic ecology , Invertebrates , Functional redundancy , Ocean temperature , Biology Classification
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/365792 , vital:65790 , DOI https://doi.org/10.21504/10962/365792
- Description: Analyses of taxonomic diversity patterns within coastal systems has been critical in the development of the theory of biogeography. Increasing evidence, however, shows that the variety of functions that species perform in ecosystems (rather than their taxonomic identity) is a better predictor of the influence of the environment on the species. This information has been useful in predictive ecology leading to the development of trait-based approaches (TBA). Until the late 1970s, however, limited effort (particularly in marine systems) was channeled towards patterns in functional species traits and how they may be affected by changes in environmental gradients. Here, I mapped the functional biogeography of the South African coastline based on a suite of species' reproduction and development traits. Because species composition is one of the key tools used by zoogeographers to map species distribution patterns, I expected lower variability in trait composition within main biogeographic regions than in intervening transition zones based on the habitat templet theory and following the biomass ratio and limiting similarity hypotheses. In brief, the habitat templet theory proposes that “the habitat provides a templet upon which evolution forges species characteristics”, while the biomass ratio hypothesis assumes that the most abundant species traits determine ecosystem functioning. The limiting similarity hypothesis also sometimes referred to as the niche complementarity hypothesis, however, predicts that species can coexist if their niches complement one another. In light of the habitat being an evolutionary templet, abiotic and biotic habitat patterns were measured as nearshore SST and chlorophyll-a gradients, respectively. I expected the SST gradient to act as the stronger key filter of trait diversification because temperature is often considered the most influential environmental factor affecting species survival with seasonality of SST affecting the timing of spawning and along with food availability, possibly influencing fecundity. Functional trait data were thus compiled for macroinvertebrate species collected from fifty-two rocky shore sites from three main bioregions (east, south, and west) and two transition zones (south-west and south-east). Biological trait analysis and functional diversity indices were used to evaluate how traits related to species development and reproduction respond to temperature and chlorophyll -a (used as a proxy for food availability) gradients along the coastline. GLMM and hierarchical cluster analyses showed distinct patterns/shifts in SST and chlorophyll-a gradients across bioregions, with two main breaks in SST separating the east and south-east overlap (SEO) bioregions from the south, south-west overlap (SWO) and west bioregions. In contrast, chlorophyll-a exhibited three major breaks with the east, SEO–south–SWO, and west clustering independently of each other. The RLQ analysis (a type of co-inertia analysis) which simultaneously ordinates 3-matrix datasets [i.e., (environment × site[R]), (species × site[L]) and (species × traits [Q])] showed that the higher SST gradient on the east and SEO promoted higher abundance and biomass of simultaneous hermaphrodites while higher chlorophyll-a gradients on the SWO and west coasts strongly promoted reproductive maturity at larger-sizes. The combined fourth-corner analyses showed that the modalities within the development trait domain responding to chlorophyll-a gradients primarily included filter feeders, sessile and swimming species and also species living on the infratidal zone. In addition, the reproduction trait domain showed higher sensitivity and association to differences in chlorophyll-a and SST gradients than development traits. Overall, SST and chlorophyll-a gradients influenced the distribution of the most dominant traits as indicated by shifts in community-weighted mean trait values across bioregions. This suggests the importance of habitat filtering on coastal species reproduction. A separate study evaluating the influence of large-scale biogeographic effects vs the micro-scale biogenic habitat structure offered by coralline seaweeds across 24 sites revealed some notable effects of both factors on the diversity and abundance of macroalgal epifauna. There was a notable biogeographic influence on epifauna, with the SEO recording the highest epifaunal species richness and abundance, followed by the south coast, then the SWO and lastly the west coast. In addition, the total biomass gradient of the corallines followed a similar trend. The epifauna however, showed no host-specificity, illustrating that epifauna may not be species–centric as commonly assumed, and the higher diversity of epifaunal diversity may well be simply because those corallines are the available habitat within the sampled part of the coastline. Lastly, macroinvertebrate trait distribution on the South African coastline confirms that the habitat, particularly the biotic filter (in this case chl-a) provides a templet upon which evolution forges species traits. However, since temperature is a proxy for nutrient availability (cold upwelling brings nutrients), then temperature drives chlorophyll-a. Subsequently this means the abiotic component indirectly drives trait distribution by influencing the biotic environment (chl-a). For epifauna species, also, the coralline diversity and composition can also be regarded as a biotic filter influencing the epifaunal abundances and composition across different bioregions. Moreover, since temperature is regarded as a conservative trait in seaweeds, temperature tolerance defines the biogeographical boundaries of seaweeds, therefore temperature may be indirectly affecting epifauna abundances through coralline species diversity and biomass. In summary, considering the deterministic processes governing ecosystem functioning and community assemblage, the mass ratio and limiting similarity hypotheses showed complementary effects. Different bioregions provided variable support for these two hypotheses, but overall, the mass ratio hypothesis (weighted by species biomass) received stronger support and may be more meaningful to the interpretation of ecosystem functioning and persistence within rocky shore systems. Lastly, although, the SWO showed some of the characteristics of a subtraction zone based on the relatively low abundance, diversity, and biomass measures. Nonetheless, there was evidence of high functional redundancy across all other four bioregions. This suggests that in the context of development and reproduction traits, the rocky shore ecosystem along the SA coastline may be functionally stable at this stage. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
Genetic analysis and field application of a UV-tolerant strain of CrleGV for improved control of Thaumatotibia leucotreta
- Authors: Bennett, Tahnee Tashia
- Date: 2022-10-14
- Subjects: Cryptophlebia leucotreta Biological control , Pests Integrated control , Biological pest control agents , Ultraviolet radiation , Oligonucleotides
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362741 , vital:65358
- Description: Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), also known as false codling moth (FCM), is indigenous to sub-Saharan Africa. Thaumatotibia leucotreta has been controlled through an integrated pest management (IPM) programme, which includes chemical control, sterile insect technique (SIT), cultural and biological control. As part of the biological control, a key component is the use of Cryptophlebia leucotreta granulovirus (CrleGV-SA). Currently, CryptogranTM, a commercial formulation of CrleGV, is the preferred product to use in South Africa for the control of T. leucotreta. The registration of the biopesticide Cryptogran (River bioscience, South Africa) was established after conducting extensive field trials with CrleGV-SA. One of the major factors affecting the baculovirus efficacy in the field is UV irradiation. A UV-tolerant Cryptophlebia leucotreta granulovirus (CrleGV-SA-C5) isolate was isolated after consecutive cycles of UV exposure. This UV-tolerant isolate is genetically distinct from the CrleGV-SA isolate. The CrleGV-SA-C5 isolate has the potential as a biological control agent. The control of T. leucotreta in South Africa could be improved by the development of novel isolates into new biopesticide formulations. To date, there has not been any field trials conducted on the CrleGV-SA-C5 isolate. Therefore, it is important to determine the biological and genetic stability of this isolate and to conduct field trials with CrleGV-SA- C5 to test the efficacy of the isolate before possible production into a biopesticide. A de novo assembly was conducted to reassemble the genome of CrleGV-SA-C5 which was followed by a sequence comparison with the CrleGV-SA genome. The identification of SNPs, led to the design of oligonucleotides flanking the regions where the SNPs were detected. Polymerase chain reaction amplification of the target regions was conducted using the oligonucleotides. After sequence comparison, seven SNPs were detected and PCR amplification was successful using the three oligonucleotides, Pif-2, HypoP and Lef-8/HP. To differentiate between CrleGV-SA-C5 and CrleGV-SA genomes and confirm the presence of the SNPs, two methods of screening were conducted. The first was the construction of six plasmids, the plasmids contained the targeted pif-2, HypoP, and the Lef-8/HP insert regions from both the CrleGV-SA-C5 and CrleGV-SA genome region where the SNPs were identified, followed by sequencing. The Five recombinant plasmids, pC5_Pif-2, pSA_Pif-2, pC5_HypoP, pSA_HypoP, and pC5_Lef-8/HP were successfully sequenced. No amplicon was obtained for one of the plasmids used as template (pSA_Lef-8/HP) and therefore the PCR product used for cloning was sequenced instead. Sequence alignment confirmed the presence of four of the five targeted SNPs in the genome of the CrleGV-SA-C5 isolate. However, of these only one SNP (UV_7) rendered a suitable marker for the differentiation between the CrleGV-SA-C5 and CrleGV-SA isolates as the SNPs, UV_2, UV_3 and UV_5, were also present in the CrleGV- SA sequences. The second screening method was a quantitative polymerase chain reaction (qPCR) melt curve analysis to differentiate between the CrleGV-SA-C5 and CrleGV-SA isolates. qPCR melt curve analysis was done using the CrleGV-SA-C5 and CrleGV-SA HypoP PCR products. This technique was unable to differentiate between the CrleGV-SA-C5 and CrleGV-SA isolates. However, this may be as a result of sequence data confirming that SNP UV_5 originally identified in the CrleGV-SA-C5 HypoP region was identical to the SNP at the same position in the CrleGV-SA HypoP region. Following the differentiation of the CrleGV-SA-C5 and CrleGV-SA isolates through two screening methods, the genetic integrity of the CrleGV-SA-C5 isolate after two virus bulk-ups was determined by PCR amplification of the target regions in the bulk-up virus followed by sequencing. Prior to virus bulk-up, surface dose bioassays were conducted on 4th instar larvae and LC50 and LC90 values of 4.01 x 106 OBs/ml and 8.75 x 109 OBs/ml respectively were obtained. The CrleGV-SA-C5 isolate was then bulked up in fourth instar T. leucotreta larvae using the LC90 value that was determined. Sequencing of the target regions from the CrleGV- SA-C5_BU2 (bulk-up 2) was conducted. Sequencing results confirmed the presence of the target SNPs in the CrleGV-SA-C5_BU2 genome. The UV-tolerance of the CrleGV-SA-C5 isolate in comparison to the CrleGV-SA isolate was evaluated by detached fruit bioassays under natural UV irradiation. Two detached fruit bioassays were set-up, a UV exposure and a non-UV exposure bioassay set-up. Three treatments were used for each bioassay set-up which were the viruses CrleGV-SA-C5 and CrleGV-SA and a ddH2O control. Statistical analysis indicated that there was no significant difference between the virus treatments in both the UV exposed detached fruit bioassay and the non-UV exposed detached fruit bioassay. This study is the second study to report on the de novo assembly of the CrleGV-SA-C5 and sequence comparison with the CrleGV-SA genome, and the first to report on the UV-tolerance of the CrleGV-SA-C5 isolate by detached fruit bioassays. Future work could involve further evaluation of intraspecific genetic variability in the CrleGV-SA-C5 isolate and to identify any additional SNPs present within the genome that can be used as suitable markers for differentiation between the CrleGV-SA-C5 and CrleGV-SA isolates. It was recognised that it is required to conduct further detached fruit bioassays and field trials, but with improved protocols, for the efficacy and UV-tolerance of the CrleGV-SA-C5 isolate to be conclusively determined. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Bennett, Tahnee Tashia
- Date: 2022-10-14
- Subjects: Cryptophlebia leucotreta Biological control , Pests Integrated control , Biological pest control agents , Ultraviolet radiation , Oligonucleotides
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362741 , vital:65358
- Description: Thaumatotibia leucotreta (Meyrick) (Lepidoptera: Tortricidae), also known as false codling moth (FCM), is indigenous to sub-Saharan Africa. Thaumatotibia leucotreta has been controlled through an integrated pest management (IPM) programme, which includes chemical control, sterile insect technique (SIT), cultural and biological control. As part of the biological control, a key component is the use of Cryptophlebia leucotreta granulovirus (CrleGV-SA). Currently, CryptogranTM, a commercial formulation of CrleGV, is the preferred product to use in South Africa for the control of T. leucotreta. The registration of the biopesticide Cryptogran (River bioscience, South Africa) was established after conducting extensive field trials with CrleGV-SA. One of the major factors affecting the baculovirus efficacy in the field is UV irradiation. A UV-tolerant Cryptophlebia leucotreta granulovirus (CrleGV-SA-C5) isolate was isolated after consecutive cycles of UV exposure. This UV-tolerant isolate is genetically distinct from the CrleGV-SA isolate. The CrleGV-SA-C5 isolate has the potential as a biological control agent. The control of T. leucotreta in South Africa could be improved by the development of novel isolates into new biopesticide formulations. To date, there has not been any field trials conducted on the CrleGV-SA-C5 isolate. Therefore, it is important to determine the biological and genetic stability of this isolate and to conduct field trials with CrleGV-SA- C5 to test the efficacy of the isolate before possible production into a biopesticide. A de novo assembly was conducted to reassemble the genome of CrleGV-SA-C5 which was followed by a sequence comparison with the CrleGV-SA genome. The identification of SNPs, led to the design of oligonucleotides flanking the regions where the SNPs were detected. Polymerase chain reaction amplification of the target regions was conducted using the oligonucleotides. After sequence comparison, seven SNPs were detected and PCR amplification was successful using the three oligonucleotides, Pif-2, HypoP and Lef-8/HP. To differentiate between CrleGV-SA-C5 and CrleGV-SA genomes and confirm the presence of the SNPs, two methods of screening were conducted. The first was the construction of six plasmids, the plasmids contained the targeted pif-2, HypoP, and the Lef-8/HP insert regions from both the CrleGV-SA-C5 and CrleGV-SA genome region where the SNPs were identified, followed by sequencing. The Five recombinant plasmids, pC5_Pif-2, pSA_Pif-2, pC5_HypoP, pSA_HypoP, and pC5_Lef-8/HP were successfully sequenced. No amplicon was obtained for one of the plasmids used as template (pSA_Lef-8/HP) and therefore the PCR product used for cloning was sequenced instead. Sequence alignment confirmed the presence of four of the five targeted SNPs in the genome of the CrleGV-SA-C5 isolate. However, of these only one SNP (UV_7) rendered a suitable marker for the differentiation between the CrleGV-SA-C5 and CrleGV-SA isolates as the SNPs, UV_2, UV_3 and UV_5, were also present in the CrleGV- SA sequences. The second screening method was a quantitative polymerase chain reaction (qPCR) melt curve analysis to differentiate between the CrleGV-SA-C5 and CrleGV-SA isolates. qPCR melt curve analysis was done using the CrleGV-SA-C5 and CrleGV-SA HypoP PCR products. This technique was unable to differentiate between the CrleGV-SA-C5 and CrleGV-SA isolates. However, this may be as a result of sequence data confirming that SNP UV_5 originally identified in the CrleGV-SA-C5 HypoP region was identical to the SNP at the same position in the CrleGV-SA HypoP region. Following the differentiation of the CrleGV-SA-C5 and CrleGV-SA isolates through two screening methods, the genetic integrity of the CrleGV-SA-C5 isolate after two virus bulk-ups was determined by PCR amplification of the target regions in the bulk-up virus followed by sequencing. Prior to virus bulk-up, surface dose bioassays were conducted on 4th instar larvae and LC50 and LC90 values of 4.01 x 106 OBs/ml and 8.75 x 109 OBs/ml respectively were obtained. The CrleGV-SA-C5 isolate was then bulked up in fourth instar T. leucotreta larvae using the LC90 value that was determined. Sequencing of the target regions from the CrleGV- SA-C5_BU2 (bulk-up 2) was conducted. Sequencing results confirmed the presence of the target SNPs in the CrleGV-SA-C5_BU2 genome. The UV-tolerance of the CrleGV-SA-C5 isolate in comparison to the CrleGV-SA isolate was evaluated by detached fruit bioassays under natural UV irradiation. Two detached fruit bioassays were set-up, a UV exposure and a non-UV exposure bioassay set-up. Three treatments were used for each bioassay set-up which were the viruses CrleGV-SA-C5 and CrleGV-SA and a ddH2O control. Statistical analysis indicated that there was no significant difference between the virus treatments in both the UV exposed detached fruit bioassay and the non-UV exposed detached fruit bioassay. This study is the second study to report on the de novo assembly of the CrleGV-SA-C5 and sequence comparison with the CrleGV-SA genome, and the first to report on the UV-tolerance of the CrleGV-SA-C5 isolate by detached fruit bioassays. Future work could involve further evaluation of intraspecific genetic variability in the CrleGV-SA-C5 isolate and to identify any additional SNPs present within the genome that can be used as suitable markers for differentiation between the CrleGV-SA-C5 and CrleGV-SA isolates. It was recognised that it is required to conduct further detached fruit bioassays and field trials, but with improved protocols, for the efficacy and UV-tolerance of the CrleGV-SA-C5 isolate to be conclusively determined. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
Implications of changing land use and introducing extralimital giraffe on vegetation in the subtropical thicket, South Africa
- Authors: Trafford, Bronwyn Kate
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422356 , vital:71935
- Description: Land use change has increased in southern Africa as many livestock farms convert to game reserves, to restore degraded and overgrazed lands. This leads to a change in herbivore communities with potential positive and negative consequences for vegetation and landscape productivity. This study aimed to look at the effect of land use change and subsequent herbivore community changes, on thicket vegetation structure, composition, and landscape productivity. To attain the study objectives, data were collected from four game reserves and their adjacent livestock farms within the Eastern Cape province in South Africa. These sites were selected because they are within the Subtropical Thicket biome (similar vegetation) and were once used for livestock farming. At each study site, vegetation composition and structure were assessed using a unique bush clump sampling technique along fence line contrasts. Six plots were sampled at each site, three plots on the game reserve lands and three plots on the adjacent livestock farmlands during the dry (July/August 2020) and wet (January/February 2021) seasons. The Normalized Difference Vegetation Index (NDVI), in-situ leaf area index (LAI) and the fraction of intercepted photosynthetically active radiation (FIPAR), were used to assess vegetation productivity between the two land use types. Additionally, diet of an extralimital herbivore, giraffe (Giraffa camelopardalis), was assessed during contrasting seasons (dry and wet) to infer the role this species might have on these landscapes. The diet of giraffes was assessed through field observations, recording plant species that giraffes were feeding on. Floristic results showed that there were no differences in vegetation structure, species composition and richness between the two land types. There was no difference in the overall diversity of plant species on the game reserves than in the adjacent livestock farms. The primary productivity was greater on the game reserves compared to the livestock farms. Field observations of giraffe feeding showed that they fed predominantly on Vachellia karroo followed by Searsia longispina. Their diets did not differ between the two seasons. My study provides an insight into the effects of changing land use and this information can be used to infer the extent to which these changes might have on restoration of degraded landscape and how land use changes may be effective in restoring the degraded thicket vegetation caused by overgrazing and overstocking of domestic livestock. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-03-29
- Authors: Trafford, Bronwyn Kate
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422356 , vital:71935
- Description: Land use change has increased in southern Africa as many livestock farms convert to game reserves, to restore degraded and overgrazed lands. This leads to a change in herbivore communities with potential positive and negative consequences for vegetation and landscape productivity. This study aimed to look at the effect of land use change and subsequent herbivore community changes, on thicket vegetation structure, composition, and landscape productivity. To attain the study objectives, data were collected from four game reserves and their adjacent livestock farms within the Eastern Cape province in South Africa. These sites were selected because they are within the Subtropical Thicket biome (similar vegetation) and were once used for livestock farming. At each study site, vegetation composition and structure were assessed using a unique bush clump sampling technique along fence line contrasts. Six plots were sampled at each site, three plots on the game reserve lands and three plots on the adjacent livestock farmlands during the dry (July/August 2020) and wet (January/February 2021) seasons. The Normalized Difference Vegetation Index (NDVI), in-situ leaf area index (LAI) and the fraction of intercepted photosynthetically active radiation (FIPAR), were used to assess vegetation productivity between the two land use types. Additionally, diet of an extralimital herbivore, giraffe (Giraffa camelopardalis), was assessed during contrasting seasons (dry and wet) to infer the role this species might have on these landscapes. The diet of giraffes was assessed through field observations, recording plant species that giraffes were feeding on. Floristic results showed that there were no differences in vegetation structure, species composition and richness between the two land types. There was no difference in the overall diversity of plant species on the game reserves than in the adjacent livestock farms. The primary productivity was greater on the game reserves compared to the livestock farms. Field observations of giraffe feeding showed that they fed predominantly on Vachellia karroo followed by Searsia longispina. Their diets did not differ between the two seasons. My study provides an insight into the effects of changing land use and this information can be used to infer the extent to which these changes might have on restoration of degraded landscape and how land use changes may be effective in restoring the degraded thicket vegetation caused by overgrazing and overstocking of domestic livestock. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-03-29
Integrative systematic structuring of the widespread psammophiid snakes (Psammophiidae): a multi-evidence species delineation approach
- Authors: Keates, Chad
- Date: 2021-10-29
- Subjects: Psammophis South Africa , Herpetology , Herpetology Africa , Molecular biology , Psammophis Classification , Psammophis Genetics , Psammophis Morphology , Psammophis Phylogeny , Morphology Mathematics , Psammophylax
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/295077 , vital:57288 , DOI 10.21504/10962/295079
- Description: Species form the foundations upon which we build our understanding of the natural world. Although a focus of much scientific attention, our understanding of species is stunted by the intrinsic ‘fuzziness’ of boundaries within nature. Due to the complexity of the evolutionary process, coupled with an ever-changing abiotic landscape, species are hard to delineate, even at the best of times. Whilst various species concepts and sophisticated delimitation methods have helped scientists tease apart species, many species complexes persist. This is because taxonomy is a discrete ordering system imposed upon the continuous and intercalated structure of life. To improve our understanding of a wide-ranging family of snakes, I investigated the taxonomy and evolutionary structuring within Psammophiidae using both molecular and morphological approaches, employing phylogenetic, phylogeographic, and morphometric analyses on the group. The systematic complexity of the family (as evidenced by past research) coupled with the group’s widespread distribution and ecological importance, made the taxon an ideal candidate for a broad-sweeping multi-level systematic analysis using multiple species delimitation methods. Additionally, in this thesis I attempted to build on the ground-breaking work of Christopher Kelly by addressing several knowledge gaps identified within the family, and in so doing, produce the most thorough evolutionary and taxonomic study of Psammophiidae possible. Given the taxonomic uncertainty associated with the family, Chapter Two used a representative sampling from every available species (near complete taxon sampling approach) in the family. The chapter used both standard and time-calibrated phylogenetic modelling and distance/threshold-based species delimitation, to elucidate the finer-level structuring within the family. Geometric morphometrics was used to determine whether there were diagnosable differences in head structure between the different genera. The final phylogenetic tree incorporated 320 samples, representing the most comprehensive phylogenetic reconstruction of the family to date. By using a near-complete taxon sampling approach, I was able to resolve previously unsupported relationships within the family whilst also identifying several novel instances of an under- and over-appreciation of species diversity within the family. Geometric morphometrics also identified clear distinctions between genera based on head shape (head width and ‘beakedness’). This chapter showcased the importance of complete taxon sampling and robust methodology for species delimitation and the deleterious effect of species concepts when implemented in isolation. In Chapter Three, I narrowed the scope of the study to focus on the genus level. Psammophylax (Fitzinger 1843) is an abundant, yet poorly studied genus of grass snakes, endemic to Africa. The generalist nature of the genus and wide-spanning distributions of the constituent species has given rise to several subspecies and a poor understanding of the taxonomic structuring within the genus. The overlapping distributions (sympatry) of many of Psammophylax species, coupled with the potential for cryptic speciation via mechanisms such as convergent evolution, made the group the ideal candidate for a broad-sweeping systematic study (as evidenced in Chapter Two). By applying the suite of analyses used in Chapter Two to the generic level, we aimed to determine the effectiveness of a multi-evidence species delineation approach when tackling systematic problems at lower taxonomic levels. A genetic phylogeny of six of the seven species was estimated using multiple phylogenetic and distance/ threshold-based species delimitation methods. To support the molecular analyses, we conducted morphological analyses on the body (traditional morphology) and head (geometric morphometrics) separately. Phylogenetic analyses recovered a similar topology to past studies, but with better resolution and node support. I found substantial genetic structuring within the genus, supported by significantly different head shapes between Ps. a. acutus and other Psammophylax species. Psammophylax a. acutus was recovered as sister to its congeners, and sequence divergence values and morphometrics supported its recognition as a new genus. Increased sampling in East Africa (Tanzania, Kenya, and Ethiopia) revealed that Psammophylax multisquamis is polyphyletic, necessitating the description of a new, morphologically cryptic, species from northern Tanzania. The distribution of Ps. multisquamis sensu stricto is likely restricted to Kenya and Ethiopia. Within this chapter, taxon-specific phylogenetic analyses yielded stronger intrageneric support as compared to Chapter Two, allowing for more defensible conclusions about taxonomical amendments. Geometric morphometrics proved similarly useful (as compared to Chapter Two) in teasing apart genera within the family but lacked the robustness to delineate species within Psammophylax with confidence, highlighting the apparent convergence of form within the genus. In Chapter Four, I investigated the evolutionary structuring within the Southern African endemic Psammophylax rhombeatus. The structural and environmental heterogeneity within the region has given rise to many morphological forms distributed throughout the country, with previous studies neglecting the associated molecular significance of these forms. Irrespective of their small sample sizes, both Chapter Two and Three identified substantial phylogenetic structuring within the species, making Ps. rhombeatus the ideal candidate for a multi-faceted systematic review, using a combination of phylogenetics, geometric morphometrics and, for the first time in this species, phylogeographic analyses. By investigating a single species, in detail, I was able to assess the effectiveness of the methodologies implemented in previous chapters on systematic sorting using the multi-evidence species delineation approach. Phylogenetic and haplotype analysis retrieved four well-supported clades: southeast South Africa (SESA), southwest South Africa (SWSA), north-eastern South Africa (NESA) and western South Africa (WSA). Although not variable enough to warrant taxonomic re-evaluation, the clades represented important genetic hotspots, with relatively high intraspecific genetic divergence values separating them, irrespective of the small geographic distances separating populations. This is likely a product of the taxon’s habitat-generalist lifestyle, enabling them to bypass vicariant barriers that might otherwise cause speciation in less versatile species. The clades are also geographically distinct, with little overlap, indicating previous vicariance, a finding that is supported by the split of Ps. rhombeatus from Ps. ocellatus in the mid-Pliocene, followed by the diversification of Ps. rhombeatus into four clades throughout the Pleistocene. The genetic structuring observed in Ps. rhombeatus may be a product of population expansion following ancient refugial isolation (potentially Last Glacial Maximum [LGM]). The molecular distinctiveness of the clades was not replicated in the morphological component of this chapter, with neither dorsal nor lateral geometric morphometric analyses of head shape showing any discernible distinctiveness based on geography. Whilst head shape has not been shown to be an effective delineator of evolutionary units at the species level (within this taxon), body colour, scalation, and snout-vent length has been linked to morphotypes within the species based on the work of Broadley (1966). These morphological groupings are loosely attributable to the molecular clades identified in the phylogenetic analyses, highlighting the complex interplay of genetic and morphological characteristics in the process of speciation, and their representation in systematic accounts. This thesis represents the most thorough evolutionary and systematic study of the family currently possible. In addition to identifying and describing both a new genus and species, this thesis also highlighted several instances of an over- and under-appreciation of species diversity within Psammophiidae. By applying a multi-evidence species delineation approach to this thesis, I show the intricacy of the evolutionary process (at various taxonomic levels) and showcase the ease to which species boundaries can be confounded when species concepts are implemented in isolation. These findings also highlighted the importance of sample size, sample range, species delimitation method on the outcome of taxonomic analyses, and their interpretation. Lastly, this thesis addressed the knowledge gaps left by Christopher Kelly’s PhD work and investigated the findings of recent papers that attempted to do the same. Whilst this study answers the questions of old, the taxon-intensive focus revealed several new knowledge gaps within the family, highlighting how much we know about snake systematics, and furthermore, how much we still need to learn about evolutionary structuring. , Thesis (PhD) -- Faculty of Science, Environmental Science, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Keates, Chad
- Date: 2021-10-29
- Subjects: Psammophis South Africa , Herpetology , Herpetology Africa , Molecular biology , Psammophis Classification , Psammophis Genetics , Psammophis Morphology , Psammophis Phylogeny , Morphology Mathematics , Psammophylax
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/295077 , vital:57288 , DOI 10.21504/10962/295079
- Description: Species form the foundations upon which we build our understanding of the natural world. Although a focus of much scientific attention, our understanding of species is stunted by the intrinsic ‘fuzziness’ of boundaries within nature. Due to the complexity of the evolutionary process, coupled with an ever-changing abiotic landscape, species are hard to delineate, even at the best of times. Whilst various species concepts and sophisticated delimitation methods have helped scientists tease apart species, many species complexes persist. This is because taxonomy is a discrete ordering system imposed upon the continuous and intercalated structure of life. To improve our understanding of a wide-ranging family of snakes, I investigated the taxonomy and evolutionary structuring within Psammophiidae using both molecular and morphological approaches, employing phylogenetic, phylogeographic, and morphometric analyses on the group. The systematic complexity of the family (as evidenced by past research) coupled with the group’s widespread distribution and ecological importance, made the taxon an ideal candidate for a broad-sweeping multi-level systematic analysis using multiple species delimitation methods. Additionally, in this thesis I attempted to build on the ground-breaking work of Christopher Kelly by addressing several knowledge gaps identified within the family, and in so doing, produce the most thorough evolutionary and taxonomic study of Psammophiidae possible. Given the taxonomic uncertainty associated with the family, Chapter Two used a representative sampling from every available species (near complete taxon sampling approach) in the family. The chapter used both standard and time-calibrated phylogenetic modelling and distance/threshold-based species delimitation, to elucidate the finer-level structuring within the family. Geometric morphometrics was used to determine whether there were diagnosable differences in head structure between the different genera. The final phylogenetic tree incorporated 320 samples, representing the most comprehensive phylogenetic reconstruction of the family to date. By using a near-complete taxon sampling approach, I was able to resolve previously unsupported relationships within the family whilst also identifying several novel instances of an under- and over-appreciation of species diversity within the family. Geometric morphometrics also identified clear distinctions between genera based on head shape (head width and ‘beakedness’). This chapter showcased the importance of complete taxon sampling and robust methodology for species delimitation and the deleterious effect of species concepts when implemented in isolation. In Chapter Three, I narrowed the scope of the study to focus on the genus level. Psammophylax (Fitzinger 1843) is an abundant, yet poorly studied genus of grass snakes, endemic to Africa. The generalist nature of the genus and wide-spanning distributions of the constituent species has given rise to several subspecies and a poor understanding of the taxonomic structuring within the genus. The overlapping distributions (sympatry) of many of Psammophylax species, coupled with the potential for cryptic speciation via mechanisms such as convergent evolution, made the group the ideal candidate for a broad-sweeping systematic study (as evidenced in Chapter Two). By applying the suite of analyses used in Chapter Two to the generic level, we aimed to determine the effectiveness of a multi-evidence species delineation approach when tackling systematic problems at lower taxonomic levels. A genetic phylogeny of six of the seven species was estimated using multiple phylogenetic and distance/ threshold-based species delimitation methods. To support the molecular analyses, we conducted morphological analyses on the body (traditional morphology) and head (geometric morphometrics) separately. Phylogenetic analyses recovered a similar topology to past studies, but with better resolution and node support. I found substantial genetic structuring within the genus, supported by significantly different head shapes between Ps. a. acutus and other Psammophylax species. Psammophylax a. acutus was recovered as sister to its congeners, and sequence divergence values and morphometrics supported its recognition as a new genus. Increased sampling in East Africa (Tanzania, Kenya, and Ethiopia) revealed that Psammophylax multisquamis is polyphyletic, necessitating the description of a new, morphologically cryptic, species from northern Tanzania. The distribution of Ps. multisquamis sensu stricto is likely restricted to Kenya and Ethiopia. Within this chapter, taxon-specific phylogenetic analyses yielded stronger intrageneric support as compared to Chapter Two, allowing for more defensible conclusions about taxonomical amendments. Geometric morphometrics proved similarly useful (as compared to Chapter Two) in teasing apart genera within the family but lacked the robustness to delineate species within Psammophylax with confidence, highlighting the apparent convergence of form within the genus. In Chapter Four, I investigated the evolutionary structuring within the Southern African endemic Psammophylax rhombeatus. The structural and environmental heterogeneity within the region has given rise to many morphological forms distributed throughout the country, with previous studies neglecting the associated molecular significance of these forms. Irrespective of their small sample sizes, both Chapter Two and Three identified substantial phylogenetic structuring within the species, making Ps. rhombeatus the ideal candidate for a multi-faceted systematic review, using a combination of phylogenetics, geometric morphometrics and, for the first time in this species, phylogeographic analyses. By investigating a single species, in detail, I was able to assess the effectiveness of the methodologies implemented in previous chapters on systematic sorting using the multi-evidence species delineation approach. Phylogenetic and haplotype analysis retrieved four well-supported clades: southeast South Africa (SESA), southwest South Africa (SWSA), north-eastern South Africa (NESA) and western South Africa (WSA). Although not variable enough to warrant taxonomic re-evaluation, the clades represented important genetic hotspots, with relatively high intraspecific genetic divergence values separating them, irrespective of the small geographic distances separating populations. This is likely a product of the taxon’s habitat-generalist lifestyle, enabling them to bypass vicariant barriers that might otherwise cause speciation in less versatile species. The clades are also geographically distinct, with little overlap, indicating previous vicariance, a finding that is supported by the split of Ps. rhombeatus from Ps. ocellatus in the mid-Pliocene, followed by the diversification of Ps. rhombeatus into four clades throughout the Pleistocene. The genetic structuring observed in Ps. rhombeatus may be a product of population expansion following ancient refugial isolation (potentially Last Glacial Maximum [LGM]). The molecular distinctiveness of the clades was not replicated in the morphological component of this chapter, with neither dorsal nor lateral geometric morphometric analyses of head shape showing any discernible distinctiveness based on geography. Whilst head shape has not been shown to be an effective delineator of evolutionary units at the species level (within this taxon), body colour, scalation, and snout-vent length has been linked to morphotypes within the species based on the work of Broadley (1966). These morphological groupings are loosely attributable to the molecular clades identified in the phylogenetic analyses, highlighting the complex interplay of genetic and morphological characteristics in the process of speciation, and their representation in systematic accounts. This thesis represents the most thorough evolutionary and systematic study of the family currently possible. In addition to identifying and describing both a new genus and species, this thesis also highlighted several instances of an over- and under-appreciation of species diversity within Psammophiidae. By applying a multi-evidence species delineation approach to this thesis, I show the intricacy of the evolutionary process (at various taxonomic levels) and showcase the ease to which species boundaries can be confounded when species concepts are implemented in isolation. These findings also highlighted the importance of sample size, sample range, species delimitation method on the outcome of taxonomic analyses, and their interpretation. Lastly, this thesis addressed the knowledge gaps left by Christopher Kelly’s PhD work and investigated the findings of recent papers that attempted to do the same. Whilst this study answers the questions of old, the taxon-intensive focus revealed several new knowledge gaps within the family, highlighting how much we know about snake systematics, and furthermore, how much we still need to learn about evolutionary structuring. , Thesis (PhD) -- Faculty of Science, Environmental Science, 2021
- Full Text:
- Date Issued: 2021-10-29
Larval assemblages in intertidal habitats: the use of artificial and natural microhabitats
- Authors: Reddy, Seshnee
- Date: 2022-10-14
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/364992 , vital:65668
- Description: Coastal habitats, and more specifically, intertidal habitats, host a unique range of biodiversity and are key areas for many fish and invertebrate species across one or more of their life stages. This is due to the provision of microhabitats which offer an escape from harsh environmental stressors and predation as well as increased food supply, hence increasing chances of survival. Due to the growing human population however, coastal habitats are being replaced by artificial structures (jetties, seawalls, piers, breakwaters) which partially or heavily fragment the natural environment through urbanisation-related expansion processes. These coastal infrastructures also have different physical properties from the natural environment and therefore tend to support different biological assemblages and can potentially alter the existing biodiversity and its functionality. The overall aim of this project was therefore to evaluate the use of artificial and natural intertidal microhabitats by fish and invertebrate larvae along the South African, Eastern Cape coastline. As independent case studies, fieldwork was conducted at an urban (Port Alfred Marina) and rocky shore (Kenton-on-Sea) site. Within each of these study sites, two replicated sheltered subsites were selected, which represented microhabitats. Samples were collected from these replicated microhabitats from September 2019 to February 2020 using light traps which targeted phototactic larval species, as well as a portable pump, for photo-neutral/negative taxa. All samples were preserved onsite in 99% ethanol and specimens were later counted and identified in the laboratory to the lowest possible taxonomic level using a stereomicroscope. Additionally, DNA barcoding was conducted on selected larval taxa for verification of morphological identification as well as contributing to the field of larval taxonomy through development of public database records. The barcoding technique was effective in positively identifying 96% and 58% of fish and invertebrate larvae sampled, respectively (overall identification success of 86%), to either family, genus or species level. Results of microhabitat use indicate higher larval abundances associated with artificial structures as compared to natural structures, with significant differences between the selected microhabitats within the rocky shores and the marina respectively, across months. High numbers of several early stage taxa were observed within the selected microhabitats in the marina, with Pinnotheres sp. (zoea) (Family: Pinnotheridae) being the most abundant invertebrate larval taxon collected at the artificial microhabitats of jetties and vertical walls. Fish larvae of Omobranchus woodi (preflexion) and Etrumeus whiteheadi (postflexion) were the most dominant at the selected artificial microhabitats within the marina. The DNA barcoding tool used in the current study to verify morphological identification proved to be instrumental in the accuracy of the reliable data collection of the early life stages present in these habitats. These results suggest that artificial structures may provide refugia for the vulnerable very early life stages of species and, in turn, play a potential facilitative role in reproductive and population connectivity which could result in replenishment of natural populations. It is therefore possible that these urban habitats could be considered as hubs for maintenance of coastal biodiversity. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Reddy, Seshnee
- Date: 2022-10-14
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/364992 , vital:65668
- Description: Coastal habitats, and more specifically, intertidal habitats, host a unique range of biodiversity and are key areas for many fish and invertebrate species across one or more of their life stages. This is due to the provision of microhabitats which offer an escape from harsh environmental stressors and predation as well as increased food supply, hence increasing chances of survival. Due to the growing human population however, coastal habitats are being replaced by artificial structures (jetties, seawalls, piers, breakwaters) which partially or heavily fragment the natural environment through urbanisation-related expansion processes. These coastal infrastructures also have different physical properties from the natural environment and therefore tend to support different biological assemblages and can potentially alter the existing biodiversity and its functionality. The overall aim of this project was therefore to evaluate the use of artificial and natural intertidal microhabitats by fish and invertebrate larvae along the South African, Eastern Cape coastline. As independent case studies, fieldwork was conducted at an urban (Port Alfred Marina) and rocky shore (Kenton-on-Sea) site. Within each of these study sites, two replicated sheltered subsites were selected, which represented microhabitats. Samples were collected from these replicated microhabitats from September 2019 to February 2020 using light traps which targeted phototactic larval species, as well as a portable pump, for photo-neutral/negative taxa. All samples were preserved onsite in 99% ethanol and specimens were later counted and identified in the laboratory to the lowest possible taxonomic level using a stereomicroscope. Additionally, DNA barcoding was conducted on selected larval taxa for verification of morphological identification as well as contributing to the field of larval taxonomy through development of public database records. The barcoding technique was effective in positively identifying 96% and 58% of fish and invertebrate larvae sampled, respectively (overall identification success of 86%), to either family, genus or species level. Results of microhabitat use indicate higher larval abundances associated with artificial structures as compared to natural structures, with significant differences between the selected microhabitats within the rocky shores and the marina respectively, across months. High numbers of several early stage taxa were observed within the selected microhabitats in the marina, with Pinnotheres sp. (zoea) (Family: Pinnotheridae) being the most abundant invertebrate larval taxon collected at the artificial microhabitats of jetties and vertical walls. Fish larvae of Omobranchus woodi (preflexion) and Etrumeus whiteheadi (postflexion) were the most dominant at the selected artificial microhabitats within the marina. The DNA barcoding tool used in the current study to verify morphological identification proved to be instrumental in the accuracy of the reliable data collection of the early life stages present in these habitats. These results suggest that artificial structures may provide refugia for the vulnerable very early life stages of species and, in turn, play a potential facilitative role in reproductive and population connectivity which could result in replenishment of natural populations. It is therefore possible that these urban habitats could be considered as hubs for maintenance of coastal biodiversity. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
Microbial and extracellular polymeric substance dynamics in arid–zone temporary pan ecosystems
- Authors: Bute, Tafara Frank
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422258 , vital:71925
- Description: Microbial communities of bacteria, viruses, algae, protozoans and fungi participate profoundly in aquatic systems, particularly in mediating processes such as primary production, decomposition, and biogeochemical cycles. In addition, microbiomes produce extracellular polymeric substances (EPS) which encompass a hydrated exopolymer mainly constituted of carbohydrates and proteins. The exopolymer aid proliferation and persistence of biofilms on their resident surfaces. There is however paucity of data on functional diversity of microbiomes in arid zone temporary wetlands with previous research having mainly focused on permanent systems in the northern hemisphere. In the face of ongoing climatic changes and anthropogenic threats to wetlands, it is imperative to assess the health status of aquatic systems in relation to microbial productivity dynamics. In this thesis, colorimetric methods and sequence–based metagenomics were conducted to quantify microbial EPS production and bacterial metagenome functions, respectively. This study was conducted in Khakhea–Bray region (North–West, South Africa) in June 2021 and January 2022 with a focus on evaluating microbial patterns of distribution between seasons (i.e., Dry and Wet) and varying depth i.e., deepest zones (Deep), intermediate depth (Mid) and shallowest regions (Edge). Additionally, potential relationships between EPS and either water content or organic matter content (OM content) were evaluated. In this study it was hypothesized that wet phases and deeper zones will have high EPS production and support more functions in comparison to shallowest regions and dry phases. Carbohydrates and proteins were quantified using the Dubois method and modified Lowry procedure, respectively. Carbohydrates generally occurred in higher proportions than proteins, suggesting that EPS found in these systems was largely diatom produced. The wet phases (wet season and inundation periods) supported more EPS production compared to the dry phases. The results of principal components analysis (PCA) and Spearman’s correlations suggested that EPS was highly correlated with sediment water content among other assessed variables. No significant associations were established between EPS and organic matter content. Spatial distribution of EPS demonstrated similar patterns between the deepest (Deep) and the intermediate depth zones (Mid) however the shallow regions (Edge) had significantly lower concentrations. Bacterial characterization was established by amplification of the 16S rRNA gene using illumina–sequencing protocol. Enzyme functions associated with biogeochemical pathways were predicted in PICRUSt2 bioinformatics pipeline. A total of 15 042 Unique Amplicon Sequence Variants (ASVs) were observed to be affiliated to 51 bacterial phyla and 1 127 genera. All top genera had commonality in heat tolerance. Firmicutes, dominated at phyla level with 59 % (mean ± sd, 19 ± 13 %) relative abundance followed by Actinobacteria and Proteobacteria both at 34 % (18 ± 7 %) and (18 ± 6 %), respectively. Microbial diversity matrices highlighted significant differences in beta diversity more than alpha diversity. Bacterial microbiomes were more distinct between seasons compared to within season, suggesting that functions were seasonally driven. These findings were supported by highest rates of denitrification, carbohydrate degradation and EPS production by core microbiomes in the wet season as compared to low rates of nitrogen mineralisation, carbon fixation and nitrification in the dry season. The present findings represent a first attempt in evaluating sequence–based metagenomics in semi–arid southern African temporary pan ecosystem. Both microbial EPS and bacterial functional potential were highly driven by water availability, with highest rates mainly associated with maximum inundation compared to dry states of pans. It can therefore be suggested that extended dry periods are threatening to microbially mediated processes in temporary wetlands, with implications to loss of biodiversity due to desiccation resulting in poor nutrient cycling. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-03-29
- Authors: Bute, Tafara Frank
- Date: 2023-03-29
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/422258 , vital:71925
- Description: Microbial communities of bacteria, viruses, algae, protozoans and fungi participate profoundly in aquatic systems, particularly in mediating processes such as primary production, decomposition, and biogeochemical cycles. In addition, microbiomes produce extracellular polymeric substances (EPS) which encompass a hydrated exopolymer mainly constituted of carbohydrates and proteins. The exopolymer aid proliferation and persistence of biofilms on their resident surfaces. There is however paucity of data on functional diversity of microbiomes in arid zone temporary wetlands with previous research having mainly focused on permanent systems in the northern hemisphere. In the face of ongoing climatic changes and anthropogenic threats to wetlands, it is imperative to assess the health status of aquatic systems in relation to microbial productivity dynamics. In this thesis, colorimetric methods and sequence–based metagenomics were conducted to quantify microbial EPS production and bacterial metagenome functions, respectively. This study was conducted in Khakhea–Bray region (North–West, South Africa) in June 2021 and January 2022 with a focus on evaluating microbial patterns of distribution between seasons (i.e., Dry and Wet) and varying depth i.e., deepest zones (Deep), intermediate depth (Mid) and shallowest regions (Edge). Additionally, potential relationships between EPS and either water content or organic matter content (OM content) were evaluated. In this study it was hypothesized that wet phases and deeper zones will have high EPS production and support more functions in comparison to shallowest regions and dry phases. Carbohydrates and proteins were quantified using the Dubois method and modified Lowry procedure, respectively. Carbohydrates generally occurred in higher proportions than proteins, suggesting that EPS found in these systems was largely diatom produced. The wet phases (wet season and inundation periods) supported more EPS production compared to the dry phases. The results of principal components analysis (PCA) and Spearman’s correlations suggested that EPS was highly correlated with sediment water content among other assessed variables. No significant associations were established between EPS and organic matter content. Spatial distribution of EPS demonstrated similar patterns between the deepest (Deep) and the intermediate depth zones (Mid) however the shallow regions (Edge) had significantly lower concentrations. Bacterial characterization was established by amplification of the 16S rRNA gene using illumina–sequencing protocol. Enzyme functions associated with biogeochemical pathways were predicted in PICRUSt2 bioinformatics pipeline. A total of 15 042 Unique Amplicon Sequence Variants (ASVs) were observed to be affiliated to 51 bacterial phyla and 1 127 genera. All top genera had commonality in heat tolerance. Firmicutes, dominated at phyla level with 59 % (mean ± sd, 19 ± 13 %) relative abundance followed by Actinobacteria and Proteobacteria both at 34 % (18 ± 7 %) and (18 ± 6 %), respectively. Microbial diversity matrices highlighted significant differences in beta diversity more than alpha diversity. Bacterial microbiomes were more distinct between seasons compared to within season, suggesting that functions were seasonally driven. These findings were supported by highest rates of denitrification, carbohydrate degradation and EPS production by core microbiomes in the wet season as compared to low rates of nitrogen mineralisation, carbon fixation and nitrification in the dry season. The present findings represent a first attempt in evaluating sequence–based metagenomics in semi–arid southern African temporary pan ecosystem. Both microbial EPS and bacterial functional potential were highly driven by water availability, with highest rates mainly associated with maximum inundation compared to dry states of pans. It can therefore be suggested that extended dry periods are threatening to microbially mediated processes in temporary wetlands, with implications to loss of biodiversity due to desiccation resulting in poor nutrient cycling. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-03-29
Native-range studies on insect herbivores associated with African Lovegrass (Eragrostis curvula) in South Africa: prospects for biological control in Australia
- Authors: Yell, Liam Dougal
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424446 , vital:72154
- Description: Eragrostis curvula (Schrad.) Nees. (African Lovegrass) is an African native species of grass that was intentionally introduced for pasture in Australia. It has since escaped cultivation and has become widespread and highly invasive. Eragrostis curvula has been recorded in every state and territory in Australia where it has altered fire regimes, disrupted nutrient cycles and can reduce livestock carrying capacity by up to 50%. The Centre for Biological Control at Rhodes University and the New South Wales Department of Primary Industries have been working in collaboration to identify and screen herbivorous insects as biological control agents for E. curvula in Australia. Native-range surveys were conducted between 2021 and 2022 on E. curvula at twenty-two sites across South Africa to identify herbivorous natural enemies associated with it. Species accumulation curves were generated to ensure adequate sampling was performed to identify all the insects associated with E. curvula. Twenty-nine non-target grass species were surveyed simultaneously to determine the field-host range of the natural enemies associated with the target weed. Herbivorous natural enemies were prioritised as possible biological control agents against E. curvula in Australia based on field-host range, predicted efficacy and climatic suitability. Four insect species were consistently found on E. curvula, two of which were herbivorous, as well as a parasitoid and a detritivore. Species accumulation curves show that the insect community was adequately sampled in South Africa. The two herbivorous insects were identified to the lowest taxonomic level using COI barcoding. Both species are undescribed phytophagous wasps in the genus Tetramesa (Hymenoptera: Eurytomidae). Because Tetramesa species have been shown to be host specific and highly damaging in previous biological control programs for other invasive grass weeds, we assessed their suitability as candidate biological control agents for use on E. curvula in Australia. Both Tetramesa species (“sp. 4” and “sp. 5”) were found on several native congeners under field conditions in South Africa. Congeneric South African-native non-target grass species were used as phylogenetic proxies to assess the risk posed to Australian native Eragrostis species. This highlighted three non-target Australian native Eragrostis species, namely: E. parviflora (R. Br.) Trin., E. leptocarpa Benth. fl., and E. trachycarpa Benth., that are at risk of being attacked by the two candidate agents based on their phylogenetic proximity to E. curvula. Predicted efficacy trials were conducted at five long-term repeat survey sites and revealed that Tetramesa sp. 4 does not reduce the probability of E. curvula tiller survival or reproduction, while Tetramesa sp. 5 does not reduce the probability of tiller reproduction but does increase the probability of tiller survival. This result was unexpected and may be a plant compensatory response to herbivory. The sites where both Tetramesa species were collected in South Africa are climatically similar to the invaded range of E. curvula in Australia, and as such, the Tetramesa spp. are likely to be suitably adapted to the climate where they would be released in Australia. These results suggest that both Tetramesa species associated with E. curvula may have too broad a host range to be used as biological control agents in Australia. However, further quarantine-based host-range assessments on Australian native Eragrostis species are recommended to confirm this. The field-based methods used in this study have reduced the number of insect and plant species that host-range assessments will be required to be performed on, thus preventing wasted resources. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
- Authors: Yell, Liam Dougal
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424446 , vital:72154
- Description: Eragrostis curvula (Schrad.) Nees. (African Lovegrass) is an African native species of grass that was intentionally introduced for pasture in Australia. It has since escaped cultivation and has become widespread and highly invasive. Eragrostis curvula has been recorded in every state and territory in Australia where it has altered fire regimes, disrupted nutrient cycles and can reduce livestock carrying capacity by up to 50%. The Centre for Biological Control at Rhodes University and the New South Wales Department of Primary Industries have been working in collaboration to identify and screen herbivorous insects as biological control agents for E. curvula in Australia. Native-range surveys were conducted between 2021 and 2022 on E. curvula at twenty-two sites across South Africa to identify herbivorous natural enemies associated with it. Species accumulation curves were generated to ensure adequate sampling was performed to identify all the insects associated with E. curvula. Twenty-nine non-target grass species were surveyed simultaneously to determine the field-host range of the natural enemies associated with the target weed. Herbivorous natural enemies were prioritised as possible biological control agents against E. curvula in Australia based on field-host range, predicted efficacy and climatic suitability. Four insect species were consistently found on E. curvula, two of which were herbivorous, as well as a parasitoid and a detritivore. Species accumulation curves show that the insect community was adequately sampled in South Africa. The two herbivorous insects were identified to the lowest taxonomic level using COI barcoding. Both species are undescribed phytophagous wasps in the genus Tetramesa (Hymenoptera: Eurytomidae). Because Tetramesa species have been shown to be host specific and highly damaging in previous biological control programs for other invasive grass weeds, we assessed their suitability as candidate biological control agents for use on E. curvula in Australia. Both Tetramesa species (“sp. 4” and “sp. 5”) were found on several native congeners under field conditions in South Africa. Congeneric South African-native non-target grass species were used as phylogenetic proxies to assess the risk posed to Australian native Eragrostis species. This highlighted three non-target Australian native Eragrostis species, namely: E. parviflora (R. Br.) Trin., E. leptocarpa Benth. fl., and E. trachycarpa Benth., that are at risk of being attacked by the two candidate agents based on their phylogenetic proximity to E. curvula. Predicted efficacy trials were conducted at five long-term repeat survey sites and revealed that Tetramesa sp. 4 does not reduce the probability of E. curvula tiller survival or reproduction, while Tetramesa sp. 5 does not reduce the probability of tiller reproduction but does increase the probability of tiller survival. This result was unexpected and may be a plant compensatory response to herbivory. The sites where both Tetramesa species were collected in South Africa are climatically similar to the invaded range of E. curvula in Australia, and as such, the Tetramesa spp. are likely to be suitably adapted to the climate where they would be released in Australia. These results suggest that both Tetramesa species associated with E. curvula may have too broad a host range to be used as biological control agents in Australia. However, further quarantine-based host-range assessments on Australian native Eragrostis species are recommended to confirm this. The field-based methods used in this study have reduced the number of insect and plant species that host-range assessments will be required to be performed on, thus preventing wasted resources. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
Phylogeography of two small owl species in South Africa: population genetics and phenotypic variation in the African Barred Owlet (Glaucidium capense) and the African Scops Owl (Otus senegalensis)
- Authors: Balmer, Jonathan Peter
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424369 , vital:72147
- Description: Embargoed. Expected release date in 2025. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
- Authors: Balmer, Jonathan Peter
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424369 , vital:72147
- Description: Embargoed. Expected release date in 2025. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
Phytoplankton and aquatic macroinvertebrate assemblages from coastal and inland lakes of South Africa
- Authors: Nkibi, Esethu
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424435 , vital:72153
- Description: Freshwater lakes are generally defined as permanent natural standing water bodies, with some of them having a direct and indirect connection with groundwater, rivers, and the ocean. Freshwater lakes provide essential socio-economic and ecological goods and services including recreation, aesthetic, support aquatic biodiversity, food in a form of fisheries and water for domestic use. Given their critical role in sustainability in providing socio-economic services, freshwater lakes are among the most threatened ecosystems globally due to intense human impacts over the last decades. South Africa has limited freshwater lakes, which according to the National Biodiversity Assessment (NBA 2018), we know little about their current biology except historic aquatic biodiversity studies conducted in the early 1940s. There are no management strategies in place to protect and conserve freshwater lake biodiversity and important ecosystem services. This thesis aims to: (1) produce a biodiversity inventory of phytoplankton and aquatic macroinvertebrate species and, (2) investigate important environmental drivers responsible for phytoplankton and aquatic macroinvertebrate species composition from six South African freshwater lakes. It was hypothesized that the three lake types will show different phytoplankton and aquatic macroinvertebrates species composition attributed by the geographical region (coastal and inland lake) and related physico-chemical parameters. Study sites consisted of two Northern KwaZulu-Natal coastal lakes (hereafter Coastal Lakes, CL) i.e., Lake Sibaya, Lake Mzingazi; two fresh inland lakes (hereafter Fresh Inland Lakes, FIL) i.e., Lake Banagher fresh and Lake Tevrede Se Pan; and two inland salt lakes (hereafter Salt Inland Lakes, SIL) i.e., Lake Banagher salt and Lake Chrissiesmeer, all inland lakes are situated in Mpumalanga province, together with other Pans making up the Mpumalanga Lake District of South Africa. The study sites were categorized based on their geographical position i.e., coastal vs inland and physico-chemical characteristics i.e., the presence and absence of aquatic vegetation, dominate substrate, salinity and different physico-chemical concentration i.e., Temperature, Dissolved Oxygen. Aquatic macroinvertebrates were collected from four littoral zone sites (< 1-meter depth) around each lake, whereas phytoplankton samples were collected from four water column sites (> 5-meters depth) and (0.5-meter depth) from the water surface at each lake during summer and winter season. The results were consistent with our hypothesis that both phytoplankton and aquatic macroinvertebrate species composition were influenced by physico-chemical parameters and that the differences in salinity concentration and aquatic vegetation between CL, FIL, and SIL were the driving factors for phytoplankton and aquatic macroinvertebrate species composition. In summary, one hundred and twenty-two phytoplankton taxa were collected and identified during this study, belonging to seven Phyla which included Chlorophyta, Bacillariophyta, Cyanophyta, Chrysophyta, Dinophyta, Euglenophyta, and Cryptophyta. The most abundant phytoplankton groups were Bacillariophyta and Chlorophyta. Phytoplankton relative taxa abundance, Pielou’s evenness, taxa richness, and Shannon diversity were significantly different between lake types. Aquatic macroinvertebrates, on the other hand, summed up to 10 orders, 67 families, and 80 taxa. The most abundant group were the order Coleoptera, Hemiptera, Odonata, and Gastropoda. Aquatic macroinvertebrate relative taxa abundance, taxa richness, and Shannon diversity were also significantly different between lake types. Aquatic macroinvertebrate relative taxa abundance, Pielous evenness, and Shannon diversity index were not significant between seasons, and only taxa richness was significant. Canonical analysis of principal coordinates (CAP) results further showed unique and distinct phytoplankton and aquatic macroinvertebrates community composition between lake types. The present study provides baseline biodiversity inventory (or species list) for important lake ecosystems biological indicators i.e., phytoplankton and aquatic macroinvertebrates and species composition in relation to lake type for six freshwater lakes in South Africa. Furthermore, the study provides empirical evidence that will inform policy and the development of management strategies for freshwater lakes in South Africa which is currently missing. The current study will also contribute to the next National Biodiversity Assessment Report (2024), concerning the freshwater lakes biological data deficiency noted in the previous NBA (2018) report. The study will also fill up the gaps to better understand species composition in lake systems and how they function which is currently limited. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
- Authors: Nkibi, Esethu
- Date: 2023-10-13
- Subjects: Uncatalogued
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/424435 , vital:72153
- Description: Freshwater lakes are generally defined as permanent natural standing water bodies, with some of them having a direct and indirect connection with groundwater, rivers, and the ocean. Freshwater lakes provide essential socio-economic and ecological goods and services including recreation, aesthetic, support aquatic biodiversity, food in a form of fisheries and water for domestic use. Given their critical role in sustainability in providing socio-economic services, freshwater lakes are among the most threatened ecosystems globally due to intense human impacts over the last decades. South Africa has limited freshwater lakes, which according to the National Biodiversity Assessment (NBA 2018), we know little about their current biology except historic aquatic biodiversity studies conducted in the early 1940s. There are no management strategies in place to protect and conserve freshwater lake biodiversity and important ecosystem services. This thesis aims to: (1) produce a biodiversity inventory of phytoplankton and aquatic macroinvertebrate species and, (2) investigate important environmental drivers responsible for phytoplankton and aquatic macroinvertebrate species composition from six South African freshwater lakes. It was hypothesized that the three lake types will show different phytoplankton and aquatic macroinvertebrates species composition attributed by the geographical region (coastal and inland lake) and related physico-chemical parameters. Study sites consisted of two Northern KwaZulu-Natal coastal lakes (hereafter Coastal Lakes, CL) i.e., Lake Sibaya, Lake Mzingazi; two fresh inland lakes (hereafter Fresh Inland Lakes, FIL) i.e., Lake Banagher fresh and Lake Tevrede Se Pan; and two inland salt lakes (hereafter Salt Inland Lakes, SIL) i.e., Lake Banagher salt and Lake Chrissiesmeer, all inland lakes are situated in Mpumalanga province, together with other Pans making up the Mpumalanga Lake District of South Africa. The study sites were categorized based on their geographical position i.e., coastal vs inland and physico-chemical characteristics i.e., the presence and absence of aquatic vegetation, dominate substrate, salinity and different physico-chemical concentration i.e., Temperature, Dissolved Oxygen. Aquatic macroinvertebrates were collected from four littoral zone sites (< 1-meter depth) around each lake, whereas phytoplankton samples were collected from four water column sites (> 5-meters depth) and (0.5-meter depth) from the water surface at each lake during summer and winter season. The results were consistent with our hypothesis that both phytoplankton and aquatic macroinvertebrate species composition were influenced by physico-chemical parameters and that the differences in salinity concentration and aquatic vegetation between CL, FIL, and SIL were the driving factors for phytoplankton and aquatic macroinvertebrate species composition. In summary, one hundred and twenty-two phytoplankton taxa were collected and identified during this study, belonging to seven Phyla which included Chlorophyta, Bacillariophyta, Cyanophyta, Chrysophyta, Dinophyta, Euglenophyta, and Cryptophyta. The most abundant phytoplankton groups were Bacillariophyta and Chlorophyta. Phytoplankton relative taxa abundance, Pielou’s evenness, taxa richness, and Shannon diversity were significantly different between lake types. Aquatic macroinvertebrates, on the other hand, summed up to 10 orders, 67 families, and 80 taxa. The most abundant group were the order Coleoptera, Hemiptera, Odonata, and Gastropoda. Aquatic macroinvertebrate relative taxa abundance, taxa richness, and Shannon diversity were also significantly different between lake types. Aquatic macroinvertebrate relative taxa abundance, Pielous evenness, and Shannon diversity index were not significant between seasons, and only taxa richness was significant. Canonical analysis of principal coordinates (CAP) results further showed unique and distinct phytoplankton and aquatic macroinvertebrates community composition between lake types. The present study provides baseline biodiversity inventory (or species list) for important lake ecosystems biological indicators i.e., phytoplankton and aquatic macroinvertebrates and species composition in relation to lake type for six freshwater lakes in South Africa. Furthermore, the study provides empirical evidence that will inform policy and the development of management strategies for freshwater lakes in South Africa which is currently missing. The current study will also contribute to the next National Biodiversity Assessment Report (2024), concerning the freshwater lakes biological data deficiency noted in the previous NBA (2018) report. The study will also fill up the gaps to better understand species composition in lake systems and how they function which is currently limited. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2023
- Full Text:
- Date Issued: 2023-10-13
Puma (Puma concolor) diet and habitat use in south-west New Mexico
- Authors: Bernard, Kelly Monica Tandi
- Date: 2022-10-14
- Subjects: Puma Food New Mexico , Puma Habitat New Mexico , Puma Nutrition New Mexico , Puma Conservation New Mexico , Carnivorous animals New Mexico , Red deer , Elk , Mule deer , Ungulates
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362752 , vital:65359
- Description: The puma (Puma concolor) is a wide-ranging large felid species occupying an extensive geographic range throughout North and South America, and site-specific research on their diet is important for local management. Like other large felids, puma diet may differ between sexes due to size dimorphism, and between seasons due to changes in prey vulnerability and availability. This study assessed the influence of sex and season on puma diet in south-west New Mexico in terms of prey species and prey size categories. Pumas specialised on mule deer and elk throughout the year, and killed a range of other species of different sizes. The diet of the smaller female puma was nested within the diet of males, supporting the size-nested strategy. The effect of puma sex on prey species and size categories was independent of season, and vice versa, and the probability of a female making a medium-sized kill such as mule deer was higher than for males, while the probability of an extra-large kill such as elk was substantially greater for males. The probability of pumas killing either mule deer or elk in each season was similar, and greater than other species categories. Additionally, individual puma strongly influenced all prey species and size categories killed. The results from this study concur with previous findings on the importance of mule deer and elk in puma diet, and suggest that puma predation may also impact a number of other species, particularly smaller herbivores like collared peccary, and mesocarnivores such as skunks. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
- Authors: Bernard, Kelly Monica Tandi
- Date: 2022-10-14
- Subjects: Puma Food New Mexico , Puma Habitat New Mexico , Puma Nutrition New Mexico , Puma Conservation New Mexico , Carnivorous animals New Mexico , Red deer , Elk , Mule deer , Ungulates
- Language: English
- Type: Academic theses , Master's theses , text
- Identifier: http://hdl.handle.net/10962/362752 , vital:65359
- Description: The puma (Puma concolor) is a wide-ranging large felid species occupying an extensive geographic range throughout North and South America, and site-specific research on their diet is important for local management. Like other large felids, puma diet may differ between sexes due to size dimorphism, and between seasons due to changes in prey vulnerability and availability. This study assessed the influence of sex and season on puma diet in south-west New Mexico in terms of prey species and prey size categories. Pumas specialised on mule deer and elk throughout the year, and killed a range of other species of different sizes. The diet of the smaller female puma was nested within the diet of males, supporting the size-nested strategy. The effect of puma sex on prey species and size categories was independent of season, and vice versa, and the probability of a female making a medium-sized kill such as mule deer was higher than for males, while the probability of an extra-large kill such as elk was substantially greater for males. The probability of pumas killing either mule deer or elk in each season was similar, and greater than other species categories. Additionally, individual puma strongly influenced all prey species and size categories killed. The results from this study concur with previous findings on the importance of mule deer and elk in puma diet, and suggest that puma predation may also impact a number of other species, particularly smaller herbivores like collared peccary, and mesocarnivores such as skunks. , Thesis (MSc) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-10-14
Quantifying the impacts of cactus biological control agents in South Africa
- Authors: Mnqeta, Zezethu
- Date: 2022-04-08
- Subjects: Cactus Biological control South Africa , Noxious weeds South Africa , Invasive plants Biological control South Africa , Insects as biological pest control agents South Africa , Cochineal insect South Africa , Mealybugs South Africa , Agricultural productivity South Africa
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/294631 , vital:57239 , DOI 10.21504/10962/294631
- Description: Invasive alien cacti are prominent weeds that threaten indigenous biodiversity and have a negative impact on agricultural productivity in South Africa. These plants are problematic because they form dense thickets that reduce the carrying capacity of rangelands; restrict the movement of livestock and wildlife thus reducing access to shade and water sources; and are directly harmful to livestock, wildlife and people due to their sharp spines. Biological control is the most effective, affordable and environmentally friendly method to control invasive alien cacti and minimize their negative impacts. Cochineal insects (Dactylopius spp.: Dactylopiidae) and the gall-forming mealybug, Hypogeococcus sp. (Pseudococcidae) are used as biological control agents for cacti. The agents are however poor dispersers, so mass-rearing and augmentative releases are required in order to establish the agents at sites where they are needed. This study aimed to evaluate the mass-rearing and release efforts of cactus biological control in South Africa, quantify the impact of the biological control agents on cactus plant populations through long-term monitoring, and assess the benefits accrued due to the biological control agents through the perceptions of land-users. An assessment of the effectiveness of the release effort for cactus biological control agents was conducted by comparing where biological control agents have been released with the known distribution of the target weeds. Only 26% of the quarter degree squares that are known to be occupied by invasive alien cacti have had biological control agents released in them. This indicated that the mass-rearing and release efforts in South Africa are inadequate and should be increased, especially in areas where few releases have been made and many cacti are present, such as the Limpopo Province. The impact of the biological control agents on cactus plant populations was assessed by monitoring agent densities, target plant densities and target plant reproductive outputs before and after releases. Plant biomass and reproductive output were reduced by biological control agents for three of the target weeds that were assessed, while the duration of the study was too short to measure reductions for the fourth target weed. Benefits to land-users were then quantified through a questionnaire survey. Land-users perceived biological control as an effective management option, with 81% of the land-users reporting that there was less invasive alien cactus after releasing biological control agents on their land. Forty-nine percent of the land-users believed that the negative impacts of the cactus had been reduced and that they benefited more from their land since control was achieved. Since land-users were only interviewed within four years of the releases being conducted, it is expected that the percentage of land-users who gained benefits from biological control will increase in future. Ninety-seven percent of the land-users stated that the agents were safe and had not fed on any other plants or had any detrimental impacts. These perceptions indicated that land-users regarded biological control as a safe and effective method of controlling invasive alien cacti. This study confirms that biological control is an effective and safe way of controlling invasive alien Cactaceae. It is also the first to assess some of the benefits that land-users have accrued due to biological control of cactus weeds. It is however evident that a greater mass-rearing and release effort is required for South Africa to get the maximum benefits possible from the use of the biological control agents for cactus weeds that are available in the country. , Izityalo ze-cactus ezisuka kwamanye amazwe zilukhula olubalaseleyo, olwenza ingxaki kwintlobo ngeentlobo zezityalo nezilwanyana kwaye ezizityalo zinefuthe neziphumo ezingalunganga kwimveliso yezolimo eMzantsi Afrika. Ezi zizityalo ziyingxaki kuba zenza amatyholo ashinyeneyo athi anciphise umthamo wokusebenzisa umhlaba: zinqanda ukuhamba nogkukhululekileyo kwemfuyo nezilwanyana zasendle ngokwenza oko zingakwazi ukufikelela emthuzini xa kutshisa nakwimithombo yamanzi yokusela; zikwayiyo nengozi kwimfuyo, izilwanyana zasendle kunye nabantu ngenxa yamave abukhali afumaneka kwezizityalo. Ukulawula nokwehliza ubunzini nezinga lemigcipheko yezizityalo, kusetyenziswa indlela ekuthiwa yi-biological control. Lendlela yeyona ndlela isebenza ngokuphucukileyo, efikelelayo, nengenabungozi kokusingqongileyo. Izinambuzane ze- cochineal (i-Dactylopius spp.: Dactylopiidae) kunye ne-mealybug, i-Hypogeococcus sp. (Pseudococcidae) zisetyenziswe njengezixhobo ze-biological control ezinceda ukulawula ezizityalo ze-cactus zingafunekiyo. Ingxaki yazo ezizinambuzane zizixhobo ze-biological control zingentla kukuba azikwazi kuzisasaza ngokwazo ukuba zifikelele nakwizityalo ezikude ngoko ke ukukhuliswa nokukhutshwa ngobuninzi bazo kuyafuneka ukukhawulelana nalengxaki kunye nokwandisa amathuba wokuba zifikelele kuzozonke izityalo ze-cactus ekufuneka zizilawule. Olu phononongo lujolise ekuvavanyeni iinzame zokukhulisa ngobuninzi nokukhupha ezezinambuzane zizixhobo ze-bioloigical control zokulawula izityalo ze-cactus eMzantsi Afrika, ukujonga ubungakanani befuthe notshintsho elenziwa zezinambuzane zizixhobo ze-bioloigical control kwizityalo ze-cactus emva kwexesha elide lokuzijonga, kunye nokuvavanya inzuzo efunyenwe ngenxa yokulawula ezizityalo ze-cactus ngokwemibono yabasebenzisi bomhlaba. Uvavanyo lweenzame zokukhutshwa kwezixhobo zezixhobo zezinambuzane ze-bioloigical control kwizityalo ze-cactus lwenziwa ngokuthelekisa iindawo apho izixhobo zezinambuzane ze-biological control zikhutshwe khona kunye neendawo apho izityalo ze-cactus kwaziwayo ukuba ziyafumaneka khona. Yi-26% kuphela yesikwere sekota eyaziwayo ukuba kukhona izityalo ze-cactus nalapho kukhutshwe khona kwezinambuzane ezizixhobo ze-biological control. Oku kubonisa ukuba iinzame zokukhulisa nokukhutshwa kwezinambuzane ezizixhobo ze-biological control eMzantsi Afrika azanelanga kwaye kufuneka zandiswe, ngakumbi kwiindawo apho kukho ukhutsho olumbalwa olwenziweyo kunye nezityalo ze-cactus ezininzi ezifumaneka khona, njengePhondo laseLimpopo. Iimpembelelo yokukhutshwa kwezinambuzane ezizixhobo ze-biological control kwizityalo ze-cactus zavavanywa ngokujonga ubunizi bezinambuzane ezizixhobo ze-biological control, ukuxinana kwezityalo ze-cactus ekujoliswe kuzo kunye nemveliso yokuzala kwezityalo ze-cactus phambi nasemva kokuba kukhutshwe izinambuzane ezizixhobo ze-biological control. Ubungakanani bezityalo ze-cactus kunye nemveliso yokuzala ziye zacutheka emva kokukhutshwa kwezinambuzane ezizixhobo ze-biological control kwinzityalo ezintathu ze-cactus ebekujoliswe uvavanyo kuzo, ngelixa ixesha lophononongo lalifutshane kakhulu ukuvavanya unciphiso kwisityalo se-cactus sesine. Izibonelelo zabasebenzisi bomhlaba zaye zavavanywa kusetyenziswa uhlobo lwemibuzo. Abasebenzisi bomhlaba balubona ukusetyenziswa kwezinambuzane ezizixhobo ze-biological control njengendlela yolawulo olusebenzayo, yi81% yabasebenzisi bomhlaba echaze ukuba izityalo ze-cactus zecuthekile emva kokukhutshwa kwezinambuzane ezizixhobo ze-biological control emhlabeni wabo. Amashumi amane anesithoba eepesenti zabasebenzisi bomhlaba bakholelwa ukuba impembelelo ezingalunganga ze-cactus zincitshisiwe kwaye baxhamle kakhulu kumhlaba wabo okoko lwaphunyenzwa. Oludliwano-ndlebe belwenziwe kubasebenzisi bomhlaba kwisithuba seminyaka emine emva kokuba kukhutshwe izinambuzane ezizixhobo ze-biological control, kulindeleke ukuba ipesenti yabasebenzisi bomhlaba abathe bafumana izibonelelo kwi-biological control lonyuke kwixesha elizayo. Amashumi alithoba anesixhenxe ekhulwini abasebenzisi bomhlaba bachaze ukuba izinambuzane ezizixhobo ze-biological control zikhuselekile kwaye khange zidle kuzo naziphi na ezinye izityalo ezingezi eze-cactus ebekujoliswe kuzo okanye zineempembelelo eyingozi. Ezi mbono ziyabonisa ukuba abasebenzi bomhlaba bayithatha i-biological control njengendlela ekhuselekileyo nesebenzayo yokulawula izityalo ze-cactus zamanye amazwe. Olu phononongo luqinisekisa ukuba ulawulo olusebenzisa izinambuzane ezizixhobo ze-biological control yindlela esebenzayo nekhuselekileyo yokulawula iCactaceae yamanye amazwe. Ikwangolokuqala ukuvavanya ezinye zezibonelelo ezizuzwe ngabasebenzisi bomhlaba ngenxa ye-biological control yezityalo ze-cactus. Nangona kunjalo kucacile ukuba ukwandisa inzame zokukhulisa nokukhupha ngobuninzi izinambuzane ezizixhobo ze-biological control kuyafuneka ukuze uMzantsi Afrika ufumane izibonelelo eziphakamileyo enokubakho ngokusetyenziswa kwe zinambuzane ezizixhobo ze-biological control zokulawula ukhula lwe-cactus olukhoyo kweli lizwe. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
- Full Text:
- Date Issued: 2022-04-08
- Authors: Mnqeta, Zezethu
- Date: 2022-04-08
- Subjects: Cactus Biological control South Africa , Noxious weeds South Africa , Invasive plants Biological control South Africa , Insects as biological pest control agents South Africa , Cochineal insect South Africa , Mealybugs South Africa , Agricultural productivity South Africa
- Language: English
- Type: Academic theses , Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/294631 , vital:57239 , DOI 10.21504/10962/294631
- Description: Invasive alien cacti are prominent weeds that threaten indigenous biodiversity and have a negative impact on agricultural productivity in South Africa. These plants are problematic because they form dense thickets that reduce the carrying capacity of rangelands; restrict the movement of livestock and wildlife thus reducing access to shade and water sources; and are directly harmful to livestock, wildlife and people due to their sharp spines. Biological control is the most effective, affordable and environmentally friendly method to control invasive alien cacti and minimize their negative impacts. Cochineal insects (Dactylopius spp.: Dactylopiidae) and the gall-forming mealybug, Hypogeococcus sp. (Pseudococcidae) are used as biological control agents for cacti. The agents are however poor dispersers, so mass-rearing and augmentative releases are required in order to establish the agents at sites where they are needed. This study aimed to evaluate the mass-rearing and release efforts of cactus biological control in South Africa, quantify the impact of the biological control agents on cactus plant populations through long-term monitoring, and assess the benefits accrued due to the biological control agents through the perceptions of land-users. An assessment of the effectiveness of the release effort for cactus biological control agents was conducted by comparing where biological control agents have been released with the known distribution of the target weeds. Only 26% of the quarter degree squares that are known to be occupied by invasive alien cacti have had biological control agents released in them. This indicated that the mass-rearing and release efforts in South Africa are inadequate and should be increased, especially in areas where few releases have been made and many cacti are present, such as the Limpopo Province. The impact of the biological control agents on cactus plant populations was assessed by monitoring agent densities, target plant densities and target plant reproductive outputs before and after releases. Plant biomass and reproductive output were reduced by biological control agents for three of the target weeds that were assessed, while the duration of the study was too short to measure reductions for the fourth target weed. Benefits to land-users were then quantified through a questionnaire survey. Land-users perceived biological control as an effective management option, with 81% of the land-users reporting that there was less invasive alien cactus after releasing biological control agents on their land. Forty-nine percent of the land-users believed that the negative impacts of the cactus had been reduced and that they benefited more from their land since control was achieved. Since land-users were only interviewed within four years of the releases being conducted, it is expected that the percentage of land-users who gained benefits from biological control will increase in future. Ninety-seven percent of the land-users stated that the agents were safe and had not fed on any other plants or had any detrimental impacts. These perceptions indicated that land-users regarded biological control as a safe and effective method of controlling invasive alien cacti. This study confirms that biological control is an effective and safe way of controlling invasive alien Cactaceae. It is also the first to assess some of the benefits that land-users have accrued due to biological control of cactus weeds. It is however evident that a greater mass-rearing and release effort is required for South Africa to get the maximum benefits possible from the use of the biological control agents for cactus weeds that are available in the country. , Izityalo ze-cactus ezisuka kwamanye amazwe zilukhula olubalaseleyo, olwenza ingxaki kwintlobo ngeentlobo zezityalo nezilwanyana kwaye ezizityalo zinefuthe neziphumo ezingalunganga kwimveliso yezolimo eMzantsi Afrika. Ezi zizityalo ziyingxaki kuba zenza amatyholo ashinyeneyo athi anciphise umthamo wokusebenzisa umhlaba: zinqanda ukuhamba nogkukhululekileyo kwemfuyo nezilwanyana zasendle ngokwenza oko zingakwazi ukufikelela emthuzini xa kutshisa nakwimithombo yamanzi yokusela; zikwayiyo nengozi kwimfuyo, izilwanyana zasendle kunye nabantu ngenxa yamave abukhali afumaneka kwezizityalo. Ukulawula nokwehliza ubunzini nezinga lemigcipheko yezizityalo, kusetyenziswa indlela ekuthiwa yi-biological control. Lendlela yeyona ndlela isebenza ngokuphucukileyo, efikelelayo, nengenabungozi kokusingqongileyo. Izinambuzane ze- cochineal (i-Dactylopius spp.: Dactylopiidae) kunye ne-mealybug, i-Hypogeococcus sp. (Pseudococcidae) zisetyenziswe njengezixhobo ze-biological control ezinceda ukulawula ezizityalo ze-cactus zingafunekiyo. Ingxaki yazo ezizinambuzane zizixhobo ze-biological control zingentla kukuba azikwazi kuzisasaza ngokwazo ukuba zifikelele nakwizityalo ezikude ngoko ke ukukhuliswa nokukhutshwa ngobuninzi bazo kuyafuneka ukukhawulelana nalengxaki kunye nokwandisa amathuba wokuba zifikelele kuzozonke izityalo ze-cactus ekufuneka zizilawule. Olu phononongo lujolise ekuvavanyeni iinzame zokukhulisa ngobuninzi nokukhupha ezezinambuzane zizixhobo ze-bioloigical control zokulawula izityalo ze-cactus eMzantsi Afrika, ukujonga ubungakanani befuthe notshintsho elenziwa zezinambuzane zizixhobo ze-bioloigical control kwizityalo ze-cactus emva kwexesha elide lokuzijonga, kunye nokuvavanya inzuzo efunyenwe ngenxa yokulawula ezizityalo ze-cactus ngokwemibono yabasebenzisi bomhlaba. Uvavanyo lweenzame zokukhutshwa kwezixhobo zezixhobo zezinambuzane ze-bioloigical control kwizityalo ze-cactus lwenziwa ngokuthelekisa iindawo apho izixhobo zezinambuzane ze-biological control zikhutshwe khona kunye neendawo apho izityalo ze-cactus kwaziwayo ukuba ziyafumaneka khona. Yi-26% kuphela yesikwere sekota eyaziwayo ukuba kukhona izityalo ze-cactus nalapho kukhutshwe khona kwezinambuzane ezizixhobo ze-biological control. Oku kubonisa ukuba iinzame zokukhulisa nokukhutshwa kwezinambuzane ezizixhobo ze-biological control eMzantsi Afrika azanelanga kwaye kufuneka zandiswe, ngakumbi kwiindawo apho kukho ukhutsho olumbalwa olwenziweyo kunye nezityalo ze-cactus ezininzi ezifumaneka khona, njengePhondo laseLimpopo. Iimpembelelo yokukhutshwa kwezinambuzane ezizixhobo ze-biological control kwizityalo ze-cactus zavavanywa ngokujonga ubunizi bezinambuzane ezizixhobo ze-biological control, ukuxinana kwezityalo ze-cactus ekujoliswe kuzo kunye nemveliso yokuzala kwezityalo ze-cactus phambi nasemva kokuba kukhutshwe izinambuzane ezizixhobo ze-biological control. Ubungakanani bezityalo ze-cactus kunye nemveliso yokuzala ziye zacutheka emva kokukhutshwa kwezinambuzane ezizixhobo ze-biological control kwinzityalo ezintathu ze-cactus ebekujoliswe uvavanyo kuzo, ngelixa ixesha lophononongo lalifutshane kakhulu ukuvavanya unciphiso kwisityalo se-cactus sesine. Izibonelelo zabasebenzisi bomhlaba zaye zavavanywa kusetyenziswa uhlobo lwemibuzo. Abasebenzisi bomhlaba balubona ukusetyenziswa kwezinambuzane ezizixhobo ze-biological control njengendlela yolawulo olusebenzayo, yi81% yabasebenzisi bomhlaba echaze ukuba izityalo ze-cactus zecuthekile emva kokukhutshwa kwezinambuzane ezizixhobo ze-biological control emhlabeni wabo. Amashumi amane anesithoba eepesenti zabasebenzisi bomhlaba bakholelwa ukuba impembelelo ezingalunganga ze-cactus zincitshisiwe kwaye baxhamle kakhulu kumhlaba wabo okoko lwaphunyenzwa. Oludliwano-ndlebe belwenziwe kubasebenzisi bomhlaba kwisithuba seminyaka emine emva kokuba kukhutshwe izinambuzane ezizixhobo ze-biological control, kulindeleke ukuba ipesenti yabasebenzisi bomhlaba abathe bafumana izibonelelo kwi-biological control lonyuke kwixesha elizayo. Amashumi alithoba anesixhenxe ekhulwini abasebenzisi bomhlaba bachaze ukuba izinambuzane ezizixhobo ze-biological control zikhuselekile kwaye khange zidle kuzo naziphi na ezinye izityalo ezingezi eze-cactus ebekujoliswe kuzo okanye zineempembelelo eyingozi. Ezi mbono ziyabonisa ukuba abasebenzi bomhlaba bayithatha i-biological control njengendlela ekhuselekileyo nesebenzayo yokulawula izityalo ze-cactus zamanye amazwe. Olu phononongo luqinisekisa ukuba ulawulo olusebenzisa izinambuzane ezizixhobo ze-biological control yindlela esebenzayo nekhuselekileyo yokulawula iCactaceae yamanye amazwe. Ikwangolokuqala ukuvavanya ezinye zezibonelelo ezizuzwe ngabasebenzisi bomhlaba ngenxa ye-biological control yezityalo ze-cactus. Nangona kunjalo kucacile ukuba ukwandisa inzame zokukhulisa nokukhupha ngobuninzi izinambuzane ezizixhobo ze-biological control kuyafuneka ukuze uMzantsi Afrika ufumane izibonelelo eziphakamileyo enokubakho ngokusetyenziswa kwe zinambuzane ezizixhobo ze-biological control zokulawula ukhula lwe-cactus olukhoyo kweli lizwe. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2022
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- Date Issued: 2022-04-08