Assessing the morphological and physiological adaptations of the parasitoid wasp E chthrodesis lamorali for survival in an intertidal environment
- Owen, Candice A, Coetzee, Julie A, van Noort, Simon, Austin, Andrew D
- Authors: Owen, Candice A , Coetzee, Julie A , van Noort, Simon , Austin, Andrew D
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123178 , vital:35412 , https://doi.org/10.1111/phen.12187
- Description: As a result of a variety of chemical, environmental, mechanical and physiological difficulties, insects that spend their entire life spans in the marine or intertidal region are relatively rare. The present study assesses whether morphological and physiological adaptations have evolved in a maritime parasitoidwasp species Echthrodesis lamorali Masner, 1968 (Hymenoptera: Platygastridae, Scelioninae), in response to environmental pressures on its respiratory functioning. Scanning electron and light microscopy of whole and sectioned specimens show the presence of structure-retaining taenidia in the tracheal tubes, although there is an absence of other major adaptations associated with the trachea or spiracles. Histological sectioning reveals the presence of unusual sacs in the female metasoma whose role is unknown, although they are hypothesized to most likely be linked to ovipositor control. Respirometry experiments illustrate the formation of a plastron when submerged, with the longevity of the wasps being increased by quiescence. The critical thermal range of E. lamorali is shown to be large: from −1.1 ∘C±0.16 to 45.7 ∘C±0.26 (mean±SE). Behavioural and physiological adaptations in E. lamorali appear to have evolved in response to exposure to the heterogeneous environmental conditions experienced within the intertidal zone.
- Full Text:
- Date Issued: 2017
- Authors: Owen, Candice A , Coetzee, Julie A , van Noort, Simon , Austin, Andrew D
- Date: 2017
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/123178 , vital:35412 , https://doi.org/10.1111/phen.12187
- Description: As a result of a variety of chemical, environmental, mechanical and physiological difficulties, insects that spend their entire life spans in the marine or intertidal region are relatively rare. The present study assesses whether morphological and physiological adaptations have evolved in a maritime parasitoidwasp species Echthrodesis lamorali Masner, 1968 (Hymenoptera: Platygastridae, Scelioninae), in response to environmental pressures on its respiratory functioning. Scanning electron and light microscopy of whole and sectioned specimens show the presence of structure-retaining taenidia in the tracheal tubes, although there is an absence of other major adaptations associated with the trachea or spiracles. Histological sectioning reveals the presence of unusual sacs in the female metasoma whose role is unknown, although they are hypothesized to most likely be linked to ovipositor control. Respirometry experiments illustrate the formation of a plastron when submerged, with the longevity of the wasps being increased by quiescence. The critical thermal range of E. lamorali is shown to be large: from −1.1 ∘C±0.16 to 45.7 ∘C±0.26 (mean±SE). Behavioural and physiological adaptations in E. lamorali appear to have evolved in response to exposure to the heterogeneous environmental conditions experienced within the intertidal zone.
- Full Text:
- Date Issued: 2017
The role of eutrophication in the biological control of water hyacinth, Eichhornia crassipes, in South Africa
- Coetzee, Julie A, Hill, Martin P
- Authors: Coetzee, Julie A , Hill, Martin P
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69263 , vital:29474 , https://doi.org/10.1007/s10526-011-9426-y
- Description: South Africa has some of the most eutrophic aquatic systems in the world, as a result of the adoption of an unnecessarily high 1 mg l-1 phosphorus (P) standard for all water treatment works in the 1970 s. The floating aquatic macrophyte, water hyacinth (Eichhornia crassipes (Mart.) Solms (Pontederiaceae), has taken advantage of these nutrient rich systems, becoming highly invasive and damaging. Despite the implementation of a biological control programme in South Africa, water hyacinth remains the worst aquatic weed. A meta-analysis of published and unpublished laboratory studies that investigated the combined effect of P and nitrogen (N) water nutrient concentration and control agent herbivory showed that water nutrient status was more important than herbivory in water hyacinth growth. Analysis of long-term field data collected monthly from 14 sites around South Africa between 2004 and 2005 supported these findings. Therefore, the first step in any water hyacinth control programme should be to reduce the nutrient status of the water body.
- Full Text:
- Date Issued: 2011
- Authors: Coetzee, Julie A , Hill, Martin P
- Date: 2011
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/69263 , vital:29474 , https://doi.org/10.1007/s10526-011-9426-y
- Description: South Africa has some of the most eutrophic aquatic systems in the world, as a result of the adoption of an unnecessarily high 1 mg l-1 phosphorus (P) standard for all water treatment works in the 1970 s. The floating aquatic macrophyte, water hyacinth (Eichhornia crassipes (Mart.) Solms (Pontederiaceae), has taken advantage of these nutrient rich systems, becoming highly invasive and damaging. Despite the implementation of a biological control programme in South Africa, water hyacinth remains the worst aquatic weed. A meta-analysis of published and unpublished laboratory studies that investigated the combined effect of P and nitrogen (N) water nutrient concentration and control agent herbivory showed that water nutrient status was more important than herbivory in water hyacinth growth. Analysis of long-term field data collected monthly from 14 sites around South Africa between 2004 and 2005 supported these findings. Therefore, the first step in any water hyacinth control programme should be to reduce the nutrient status of the water body.
- Full Text:
- Date Issued: 2011
First record of an indigenous South African parasitoid wasp on an imported biological control agent, the water hyacinth hopper
- Kraus, Emily, Coetzee, Julie A, van Noort, Simon, Olmi, Massimo
- Authors: Kraus, Emily , Coetzee, Julie A , van Noort, Simon , Olmi, Massimo
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/417462 , vital:71455 , xlink:href="https://doi.org/10.1080/09583157.2019.1660306"
- Description: Water hyacinth, Pontederia crassipes (Martius) [≡Eichhornia crassip es (Martius) Solms-Laubach] (Pontederiaceae), is native to South America, but has expanded its range to many other regions of the world including South Africa. Megamelus scutellaris Berg (Hemiptera: Delphacidae) was released as a biological control agent and has established in several regions. Recently, the indigenous species Echthrodelphax migratorius Benoit, (Hymenoptera: Dryinidae) was discovered in South Africa parasitising M. scutellaris. This newly discovered relationship might have repercussions for the efficacy of biological control of water hyacinth by the delphacid. The wasp may negatively impact M. scutellaris populations making it difficult for the agent to successfully manage the invasive weed. Contrarily, the parasitoid may be beneficial by keeping the M. scutellaris populations stable, serving as a natural enemy.
- Full Text:
- Date Issued: 2019
- Authors: Kraus, Emily , Coetzee, Julie A , van Noort, Simon , Olmi, Massimo
- Date: 2019
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/417462 , vital:71455 , xlink:href="https://doi.org/10.1080/09583157.2019.1660306"
- Description: Water hyacinth, Pontederia crassipes (Martius) [≡Eichhornia crassip es (Martius) Solms-Laubach] (Pontederiaceae), is native to South America, but has expanded its range to many other regions of the world including South Africa. Megamelus scutellaris Berg (Hemiptera: Delphacidae) was released as a biological control agent and has established in several regions. Recently, the indigenous species Echthrodelphax migratorius Benoit, (Hymenoptera: Dryinidae) was discovered in South Africa parasitising M. scutellaris. This newly discovered relationship might have repercussions for the efficacy of biological control of water hyacinth by the delphacid. The wasp may negatively impact M. scutellaris populations making it difficult for the agent to successfully manage the invasive weed. Contrarily, the parasitoid may be beneficial by keeping the M. scutellaris populations stable, serving as a natural enemy.
- Full Text:
- Date Issued: 2019
Life history of the maritime platygastrid Echthrodesis lamorali Masner 1968 (Hymenoptera: Platygastridae: Scelioninae)
- Authors: Owen, Candice Ann
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/837 , vital:19995 , 10.21504/10962/837
- Description: Echthrodesis lamorali Masner 1968 (Hymenoptera: Platygastridae, Scelioninae) is an intertidal parasitoid wasp that uses the eggs of the maritime spider, Desis formidabilis O.P. Cambridge 1890 (Araneae: Desidae), as a host. This species is one of only three known maritime parasitoids globally, and is the only known spider egg parasitoid that attacks its host within the intertidal region in southern Africa. Originally described from ‘The Island’, Kommetjie (Western Cape, South Africa), this shore was the only known locality of the species at the commencement of this thesis. Furthermore, the extent of the parasitism pressure the wasp exerts on D. formidabilis was largely unknown, along with its basic biology (drivers of its broad-scale and fine-scale distribution patterns; parasitism incidence; and sex ratios) and morphological and physiological adaptations for living within the frequently saltwater-inundated environment. This thesis unravelled these aspects, as well as experimentally provided data for many components of the life history of E. lamorali that had only been hypothesized by other authors, at a variety of scales, from the country-wide ecosystem, to single shores, and finally to the scale of the individual. While the distribution of E. lamorali was found to be much wider than previously thought, it remained restricted to the shores of the Cape Peninsula (Western Cape, South Africa). The host spiders were located throughout a much wider distributional range than the wasp, from East London in the east to the Peninsula, but some behavioural and morphological differences were found between those within and outside of the range of the parasitoid, suggesting range-limitation imposed by the host on E. lamorali. This limitation may be strengthened by the general lack of suitable shore types within the close vicinity of the Peninsula. Modelling using macro-climatic conditions suggested that maximum temperatures and humidities were also largely limiting to E. lamorali, although these patterns were not observable in the micro-climates in which the species survives. The wasp populations and spiders within the range of E. lamorali as identified in Chapter 2 were assessed to determine any preferences for local conditions, including location along the Peninsula, nesting sites and intertidal zones within single shores, using AICc modelling, which detected parasitism patterns in D. formidabilis and E. lamorali populations, as well as the sex ratios in the latter species. The models showed that the spider population size and distribution was more influenced by bottom-up factors such as abiotic components of the shore than by parasitism, which only showed density dependence with the host at certain scales. Both host and parasitoid populations illustrated a preference for the middle zone on single shores. Observed spider nest characteristics suggested opportunistic nesting behaviour in the species, although preference was shown for construction along an east-west orientation and in locations with low sun exposure. Along with larger population sizes on the west coast over the east coast (not reflected by E. lamorali), these observations suggest that D. formidabilis prefers cooler environments. Spider brood success was 50% in unparasitized egg-sacs, but this figure halved when E. lamorali gained access to the eggs (of which 100% within a single compartment were parasitized each time). Encapsulation of the embryo was found to be positively correlated with parasitism, indicating some form of host resistance. Resultant parasitoid broods illustrated a strong female bias in the species, as is common for this group of insects. The life history of E. lamorali was then assessed at a smaller scale, that of the individual. Scanning electron microscopy of whole E. lamorali specimens and light microscopy of sectioned specimens demonstrated no morphological adaptations in the trachea and spiracles to cope with saltwater inundation. On the other hand, respirometry experiments categorically demonstrated that the species copes with inundation through the formation of a physical gill over the full habitus, and the induction of a state of torpor to reduce metabolic needs, when submerged. This precludes the need for any further morphological adaptations. Determination of the wasp’s critical thermal tolerance illustrated a wide temperature range with a particularly cold lower limit of -1.1ºC ± 0.16, suggesting the presence of related genera or ancestors in much colder environments. With a much broader distribution than previously thought, and the inclusion of the distributional range of E. lamorali within the Table Mountain National Park, this species is being effectively conserved and managed through the umbrella-conservation of the park. Links to the host proved to vary at differing scales, proving the need for scale considerations to be included in other similar biological and ecological studies. Finally, the species showed physiological adaptation to its intertidal existence. Echthrodesis lamorali, the only discovered maritime spider egg parasitoid in Southern Africa, displayed unusual characteristics at every scale of its life history and as such, warrants further investigation.
- Full Text:
- Date Issued: 2016
- Authors: Owen, Candice Ann
- Date: 2016
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: http://hdl.handle.net/10962/837 , vital:19995 , 10.21504/10962/837
- Description: Echthrodesis lamorali Masner 1968 (Hymenoptera: Platygastridae, Scelioninae) is an intertidal parasitoid wasp that uses the eggs of the maritime spider, Desis formidabilis O.P. Cambridge 1890 (Araneae: Desidae), as a host. This species is one of only three known maritime parasitoids globally, and is the only known spider egg parasitoid that attacks its host within the intertidal region in southern Africa. Originally described from ‘The Island’, Kommetjie (Western Cape, South Africa), this shore was the only known locality of the species at the commencement of this thesis. Furthermore, the extent of the parasitism pressure the wasp exerts on D. formidabilis was largely unknown, along with its basic biology (drivers of its broad-scale and fine-scale distribution patterns; parasitism incidence; and sex ratios) and morphological and physiological adaptations for living within the frequently saltwater-inundated environment. This thesis unravelled these aspects, as well as experimentally provided data for many components of the life history of E. lamorali that had only been hypothesized by other authors, at a variety of scales, from the country-wide ecosystem, to single shores, and finally to the scale of the individual. While the distribution of E. lamorali was found to be much wider than previously thought, it remained restricted to the shores of the Cape Peninsula (Western Cape, South Africa). The host spiders were located throughout a much wider distributional range than the wasp, from East London in the east to the Peninsula, but some behavioural and morphological differences were found between those within and outside of the range of the parasitoid, suggesting range-limitation imposed by the host on E. lamorali. This limitation may be strengthened by the general lack of suitable shore types within the close vicinity of the Peninsula. Modelling using macro-climatic conditions suggested that maximum temperatures and humidities were also largely limiting to E. lamorali, although these patterns were not observable in the micro-climates in which the species survives. The wasp populations and spiders within the range of E. lamorali as identified in Chapter 2 were assessed to determine any preferences for local conditions, including location along the Peninsula, nesting sites and intertidal zones within single shores, using AICc modelling, which detected parasitism patterns in D. formidabilis and E. lamorali populations, as well as the sex ratios in the latter species. The models showed that the spider population size and distribution was more influenced by bottom-up factors such as abiotic components of the shore than by parasitism, which only showed density dependence with the host at certain scales. Both host and parasitoid populations illustrated a preference for the middle zone on single shores. Observed spider nest characteristics suggested opportunistic nesting behaviour in the species, although preference was shown for construction along an east-west orientation and in locations with low sun exposure. Along with larger population sizes on the west coast over the east coast (not reflected by E. lamorali), these observations suggest that D. formidabilis prefers cooler environments. Spider brood success was 50% in unparasitized egg-sacs, but this figure halved when E. lamorali gained access to the eggs (of which 100% within a single compartment were parasitized each time). Encapsulation of the embryo was found to be positively correlated with parasitism, indicating some form of host resistance. Resultant parasitoid broods illustrated a strong female bias in the species, as is common for this group of insects. The life history of E. lamorali was then assessed at a smaller scale, that of the individual. Scanning electron microscopy of whole E. lamorali specimens and light microscopy of sectioned specimens demonstrated no morphological adaptations in the trachea and spiracles to cope with saltwater inundation. On the other hand, respirometry experiments categorically demonstrated that the species copes with inundation through the formation of a physical gill over the full habitus, and the induction of a state of torpor to reduce metabolic needs, when submerged. This precludes the need for any further morphological adaptations. Determination of the wasp’s critical thermal tolerance illustrated a wide temperature range with a particularly cold lower limit of -1.1ºC ± 0.16, suggesting the presence of related genera or ancestors in much colder environments. With a much broader distribution than previously thought, and the inclusion of the distributional range of E. lamorali within the Table Mountain National Park, this species is being effectively conserved and managed through the umbrella-conservation of the park. Links to the host proved to vary at differing scales, proving the need for scale considerations to be included in other similar biological and ecological studies. Finally, the species showed physiological adaptation to its intertidal existence. Echthrodesis lamorali, the only discovered maritime spider egg parasitoid in Southern Africa, displayed unusual characteristics at every scale of its life history and as such, warrants further investigation.
- Full Text:
- Date Issued: 2016
First record of an indigenous South African parasitoid wasp on an imported biological control agent, the water hyacinth hopper
- Kraus, Emily C, Coetzee, Julie A, van Noort, Simon, Olmi, Massimo
- Authors: Kraus, Emily C , Coetzee, Julie A , van Noort, Simon , Olmi, Massimo
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/417700 , vital:71479 , xlink:href="https://doi.org/10.1080/09583157.2019.1660306"
- Description: Water hyacinth, Pontederia crassipes (Martius) [≡Eichhornia crassip es (Martius) Solms-Laubach] (Pontederiaceae), is native to South America, but has expanded its range to many other regions of the world including South Africa. Megamelus scutellaris Berg (Hemiptera: Delphacidae) was released as a biological control agent and has established in several regions. Recently, the indigenous species Echthrodelphax migratorius Benoit, (Hymenoptera: Dryinidae) was discovered in South Africa parasitising M. scutellaris. This newly discovered relationship might have repercussions for the efficacy of biological control of water hyacinth by the delphacid. The wasp may negatively impact M. scutellaris populations making it difficult for the agent to successfully manage the invasive weed. Contrarily, the parasitoid may be beneficial by keeping the M. scutellaris populations stable, serving as a natural enemy.
- Full Text:
- Date Issued: 2020
- Authors: Kraus, Emily C , Coetzee, Julie A , van Noort, Simon , Olmi, Massimo
- Date: 2020
- Subjects: To be catalogued
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/417700 , vital:71479 , xlink:href="https://doi.org/10.1080/09583157.2019.1660306"
- Description: Water hyacinth, Pontederia crassipes (Martius) [≡Eichhornia crassip es (Martius) Solms-Laubach] (Pontederiaceae), is native to South America, but has expanded its range to many other regions of the world including South Africa. Megamelus scutellaris Berg (Hemiptera: Delphacidae) was released as a biological control agent and has established in several regions. Recently, the indigenous species Echthrodelphax migratorius Benoit, (Hymenoptera: Dryinidae) was discovered in South Africa parasitising M. scutellaris. This newly discovered relationship might have repercussions for the efficacy of biological control of water hyacinth by the delphacid. The wasp may negatively impact M. scutellaris populations making it difficult for the agent to successfully manage the invasive weed. Contrarily, the parasitoid may be beneficial by keeping the M. scutellaris populations stable, serving as a natural enemy.
- Full Text:
- Date Issued: 2020
Interactions between figs (Ficus spp., Moraceae) and fig wasps (Chalcidoidea, Agaonidae)
- Authors: Ware, Anthony Brian
- Date: 1993
- Subjects: Fig -- South Africa Fig wasp -- South Africa Pollination Agaonidae Chalcid wasps
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5719 , http://hdl.handle.net/10962/d1005405
- Description: Fig trees (Ficus spp., Moraceae) and fig wasps (Chalcidoidea, Agaonidae) are uniquely associated. In one fig wasp group, the pollinators (Agaoninae), each species is generally host species-specific. The relationship is one of obligate mutualism where the wasps provide pollination services and in return utilises some of the ovules for larval development. Non-pollinating fig wasps (generally belonging to subfamilies other than the Agaoninae) may be gallers or parasitoids, and can also be host species-specific. In the accompanying studies we examined the factors governing the interactions between fig wasps and their host trees. Surveys of fig trees and their associated pollinating fig wasps conducted in southern Africa, Madagascar and The Comores generally confirmed their specific relationships. An examination of F. sycomorlls in Madagascar resulted in the reclassification of F. sakalavarum as a distinct species with its own specific pollinator species. Biological and chemical evidence is presented demonstrating that the pollinators were able to distinguish their hosts through volatiles which emanated from the figs when they were ready to be pollinated. Environmental factors were found to influence wasp behaviour. Ambient temperature governed the timing of wasp emergence from their natal figs. When dispersing from their natal figs, the fig wasps flew upwards and then were blown downwind. Once nearing trees bearing figs ready to be pollinated, the wasps lost height and flew upwind towards the trees. E. baijnathi females apparently avoided figs which already contained a conspecific foundress. Scanning electron microscope studies of pollinating female fig wasp antennae showed that while all the species possessed multiporous plate sensilla, in only a few species were these sensilla elongated. Multiporous plate sensilla elongation is rare or absent among other female chalcids and may have evolved within the Agaoninae in order to facilitate their location on receptive host figs. Pollinator choice specificity appears to break down in a number of cases. In the first case examined, two pollinator species were recorded from the figs of African F. sycomorus. One. C. arabicus, pollinates the figs while the other, C. galili, acts as a 'cuckoo' by utilising some of ovules for oviposition without providing pollen. In the second case three pollinating fig wasp species were recorded from the rigs of F. lutea. Two were found to be incidental visitors and were not specifically attracted to the tree. The hybrid seeds from these crosses were successfully germinated but the seedlings did not grow passed the cotyledon stage of their development. In the concluding study the consequences of Ficus phenology and the structure of the fig's unusual inflorescence on the nonpollinating fig wasp community were examined. Various factors affecting the population levels and species richness were also examined. Future possible research directions were discussed.
- Full Text:
- Date Issued: 1993
- Authors: Ware, Anthony Brian
- Date: 1993
- Subjects: Fig -- South Africa Fig wasp -- South Africa Pollination Agaonidae Chalcid wasps
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5719 , http://hdl.handle.net/10962/d1005405
- Description: Fig trees (Ficus spp., Moraceae) and fig wasps (Chalcidoidea, Agaonidae) are uniquely associated. In one fig wasp group, the pollinators (Agaoninae), each species is generally host species-specific. The relationship is one of obligate mutualism where the wasps provide pollination services and in return utilises some of the ovules for larval development. Non-pollinating fig wasps (generally belonging to subfamilies other than the Agaoninae) may be gallers or parasitoids, and can also be host species-specific. In the accompanying studies we examined the factors governing the interactions between fig wasps and their host trees. Surveys of fig trees and their associated pollinating fig wasps conducted in southern Africa, Madagascar and The Comores generally confirmed their specific relationships. An examination of F. sycomorlls in Madagascar resulted in the reclassification of F. sakalavarum as a distinct species with its own specific pollinator species. Biological and chemical evidence is presented demonstrating that the pollinators were able to distinguish their hosts through volatiles which emanated from the figs when they were ready to be pollinated. Environmental factors were found to influence wasp behaviour. Ambient temperature governed the timing of wasp emergence from their natal figs. When dispersing from their natal figs, the fig wasps flew upwards and then were blown downwind. Once nearing trees bearing figs ready to be pollinated, the wasps lost height and flew upwind towards the trees. E. baijnathi females apparently avoided figs which already contained a conspecific foundress. Scanning electron microscope studies of pollinating female fig wasp antennae showed that while all the species possessed multiporous plate sensilla, in only a few species were these sensilla elongated. Multiporous plate sensilla elongation is rare or absent among other female chalcids and may have evolved within the Agaoninae in order to facilitate their location on receptive host figs. Pollinator choice specificity appears to break down in a number of cases. In the first case examined, two pollinator species were recorded from the figs of African F. sycomorus. One. C. arabicus, pollinates the figs while the other, C. galili, acts as a 'cuckoo' by utilising some of ovules for oviposition without providing pollen. In the second case three pollinating fig wasp species were recorded from the rigs of F. lutea. Two were found to be incidental visitors and were not specifically attracted to the tree. The hybrid seeds from these crosses were successfully germinated but the seedlings did not grow passed the cotyledon stage of their development. In the concluding study the consequences of Ficus phenology and the structure of the fig's unusual inflorescence on the nonpollinating fig wasp community were examined. Various factors affecting the population levels and species richness were also examined. Future possible research directions were discussed.
- Full Text:
- Date Issued: 1993
Systematics of the Afrotropical Chalcididae (Hymenoptera: Chalcidoidea)
- Authors: Faure, Sariana
- Date: 2021-10-29
- Subjects: Uncatalogued
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/192808 , vital:45266
- Description: Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Faure, Sariana
- Date: 2021-10-29
- Subjects: Uncatalogued
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/192808 , vital:45266
- Description: Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10-29
Patterns and processes underlying evolutionary significant units in the Platypleura stridula L. species complex (Hemiptera: Cicadidae) in the Cape Floristic Region, South Africa
- Price, Benjamin W, Barker, Nigel P, Villet, Martin H
- Authors: Price, Benjamin W , Barker, Nigel P , Villet, Martin H
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6964 , http://hdl.handle.net/10962/d1012027
- Description: Cicadas have been shown to be useful organisms for examining the effects of distribution, plant association and geographical barriers on gene flow between populations. The cicadas of the Platypleura stridula species complex are restricted to the biologically diverse Cape Floristic Region (CFR) of South Africa. They are thus an excellent study group for elucidating the mechanisms by which hemipteran diversity is generated and maintained in the CFR. Phylogeographical analysis of this species complex using mitochondrial DNA Cytochrome Oxidase I (COI) and ribosomal 16S sequence data, coupled with preliminary morphological and acoustic data, resolves six clades, each of which has specific host-plant associations and distinct geographical ranges. The phylogeographical structure implies simultaneous or near-simultaneous radiation events, coupled with shifts in host-plant associations. When calibrated using published COI and 16S substitution rates typical for related insects, these lineages date back to the late Pliocene - early Pleistocene, coincident with vegetation change, altered drainage patterns and accelerated erosion in response to neotectonic crustal uplift and cyclic Pleistocene climate change, and glaciation-associated changes in climate and sea level.
- Full Text:
- Date Issued: 2007
- Authors: Price, Benjamin W , Barker, Nigel P , Villet, Martin H
- Date: 2007
- Language: English
- Type: Article
- Identifier: vital:6964 , http://hdl.handle.net/10962/d1012027
- Description: Cicadas have been shown to be useful organisms for examining the effects of distribution, plant association and geographical barriers on gene flow between populations. The cicadas of the Platypleura stridula species complex are restricted to the biologically diverse Cape Floristic Region (CFR) of South Africa. They are thus an excellent study group for elucidating the mechanisms by which hemipteran diversity is generated and maintained in the CFR. Phylogeographical analysis of this species complex using mitochondrial DNA Cytochrome Oxidase I (COI) and ribosomal 16S sequence data, coupled with preliminary morphological and acoustic data, resolves six clades, each of which has specific host-plant associations and distinct geographical ranges. The phylogeographical structure implies simultaneous or near-simultaneous radiation events, coupled with shifts in host-plant associations. When calibrated using published COI and 16S substitution rates typical for related insects, these lineages date back to the late Pliocene - early Pleistocene, coincident with vegetation change, altered drainage patterns and accelerated erosion in response to neotectonic crustal uplift and cyclic Pleistocene climate change, and glaciation-associated changes in climate and sea level.
- Full Text:
- Date Issued: 2007
The systematics and phylogenetics of the Sycoecinae (Agaonidae, Chalcidoidea, Hymenoptera)
- Authors: Noort, Simon van
- Date: 1993
- Subjects: Agaonidae Chalcid wasps Fig wasp -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5784 , http://hdl.handle.net/10962/d1005472
- Description: The Sycoecinae are a distinct and well-defined subfamily of old world fig wasps (Agaonidae, Chalcidoidea 1 Hymenoptera) , exclusively associated with the figs of Ficus species (Moraceae). The most likely sister group of the Sycoecinae was determined to be the Sycoryctini (Sycoryctinae) based largely on synapomorphies of the underside of the head. 67 sycoecine species and 3 subspecies were recognised and included in a phylogenetic analysis of the subfamily. This analysis clearly delimited six genera (four African and two extra-African), although the phylogenetic relationships between the genera were not strongly supported and remain flexible. Comparisons of the phylogeny of the Sycoecinae with the classifications of the Agaoninae and their host fig trees (Ficus, Moraceae) suggest a degree of cospeciation sensu lato. Numerous homoplasies were detected within the Sycoecinae, some of which were shared with another group of fig wasps that also enter the fig to oviposit, the Agaoninae. The anatomy of the figs apparently provides strong selection pressures that have resulted in both parallelisms and convergences within and between the two subfamilies. Among the 67 species and 3 subspecies that were recognised, 43 species and 2 subspecies are described as new. The males of three previously recognised species are also described for the first time. One generic and two specific synonyms are established together with five new combinations. Keys are provided to the genera and species, for both sexes.
- Full Text:
- Date Issued: 1993
- Authors: Noort, Simon van
- Date: 1993
- Subjects: Agaonidae Chalcid wasps Fig wasp -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5784 , http://hdl.handle.net/10962/d1005472
- Description: The Sycoecinae are a distinct and well-defined subfamily of old world fig wasps (Agaonidae, Chalcidoidea 1 Hymenoptera) , exclusively associated with the figs of Ficus species (Moraceae). The most likely sister group of the Sycoecinae was determined to be the Sycoryctini (Sycoryctinae) based largely on synapomorphies of the underside of the head. 67 sycoecine species and 3 subspecies were recognised and included in a phylogenetic analysis of the subfamily. This analysis clearly delimited six genera (four African and two extra-African), although the phylogenetic relationships between the genera were not strongly supported and remain flexible. Comparisons of the phylogeny of the Sycoecinae with the classifications of the Agaoninae and their host fig trees (Ficus, Moraceae) suggest a degree of cospeciation sensu lato. Numerous homoplasies were detected within the Sycoecinae, some of which were shared with another group of fig wasps that also enter the fig to oviposit, the Agaoninae. The anatomy of the figs apparently provides strong selection pressures that have resulted in both parallelisms and convergences within and between the two subfamilies. Among the 67 species and 3 subspecies that were recognised, 43 species and 2 subspecies are described as new. The males of three previously recognised species are also described for the first time. One generic and two specific synonyms are established together with five new combinations. Keys are provided to the genera and species, for both sexes.
- Full Text:
- Date Issued: 1993
Rhodes University Graduation Ceremony 1988
- Authors: Rhodes University
- Date: 1988
- Language: English
- Type: text
- Identifier: vital:8122 , http://hdl.handle.net/10962/d1005705
- Description: Rhodes University Graduation Ceremonies on Friday, 8 April 1988 at 8 p.m. [and] on Friday, 9 April 1988 at 10 a.m. in the 1820 Settlers National Monument. , Rhodes University East London Graduation Ceremony Saturday; 7 May 1988 at 11.30 a.m. in the Guild Theatre.
- Full Text:
- Date Issued: 1988
- Authors: Rhodes University
- Date: 1988
- Language: English
- Type: text
- Identifier: vital:8122 , http://hdl.handle.net/10962/d1005705
- Description: Rhodes University Graduation Ceremonies on Friday, 8 April 1988 at 8 p.m. [and] on Friday, 9 April 1988 at 10 a.m. in the 1820 Settlers National Monument. , Rhodes University East London Graduation Ceremony Saturday; 7 May 1988 at 11.30 a.m. in the Guild Theatre.
- Full Text:
- Date Issued: 1988
Conservation implications of fine scale population genetic structure of Ficus species in South African forests:
- Deng, Jun-Yin, van Noort, Simon, Compton, Stephen G, Chen, Yan, Greeff, Jaco M
- Authors: Deng, Jun-Yin , van Noort, Simon , Compton, Stephen G , Chen, Yan , Greeff, Jaco M
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/163838 , vital:41074 , ttps://doi.org/10.1016/j.foreco.2020.118387
- Description: Genetic considerations are rarely applied in forest conservation management strategies, but forest fragmentation can reduce pollen and seed dispersal both between and within isolated fragments. Gene flow and immigration rates determine the extent to which individual plants are related to each other at different distances from themselves. This gradation in relatedness is known as a population's fine scale spatial genetic structure (SGS). Specifically, reduced but clumped immigration from distant fragments reduces fine scale SGS, whereas reduced gene flow within fragments increases fine scale SGS. In addition, non-random mortality caused by post-dispersal ecological processes can also affect SGS. We studied the effects of fragmentation on the fine scale SGS of Ficus species with different habitat preferences and distributional ranges in an archipelago of South African forest patches.
- Full Text:
- Date Issued: 2020
- Authors: Deng, Jun-Yin , van Noort, Simon , Compton, Stephen G , Chen, Yan , Greeff, Jaco M
- Date: 2020
- Language: English
- Type: text , article
- Identifier: http://hdl.handle.net/10962/163838 , vital:41074 , ttps://doi.org/10.1016/j.foreco.2020.118387
- Description: Genetic considerations are rarely applied in forest conservation management strategies, but forest fragmentation can reduce pollen and seed dispersal both between and within isolated fragments. Gene flow and immigration rates determine the extent to which individual plants are related to each other at different distances from themselves. This gradation in relatedness is known as a population's fine scale spatial genetic structure (SGS). Specifically, reduced but clumped immigration from distant fragments reduces fine scale SGS, whereas reduced gene flow within fragments increases fine scale SGS. In addition, non-random mortality caused by post-dispersal ecological processes can also affect SGS. We studied the effects of fragmentation on the fine scale SGS of Ficus species with different habitat preferences and distributional ranges in an archipelago of South African forest patches.
- Full Text:
- Date Issued: 2020
Sperm morphology in four species of African platypleurine cicadas (Hemiptera: Cicadomorpha: Cicadidae)
- Chawanji, A S, Hodgson, Alan N, Villet, Martin H
- Authors: Chawanji, A S , Hodgson, Alan N , Villet, Martin H
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6917 , http://hdl.handle.net/10962/d1011880
- Description: Mature spermatozoa from four species of platypleurine cicadas (Albanycada albigera, Azanicada zuluensis, Platypleura capensis and P. hirtipennis) were examined by light and electron microscopy. The filiform sperm have a similar ultrastructure in all species but notable variations were found in sperm dimensions. All species produce more than one discrete length of nucleated, motile sperm, a form of polymorphism termed polymegaly. Polymegaly is expressed in two ways: sperm have bi- or trimodal head and tail lengths. The anterior parts of sperm heads are embedded in an elongate homogenous matrix forming a spermatodesm. The conical acrosome is deeply invaginated posteriorly, and sits on top of the nucleus. The acrosomal contents are differentiated internally with an electron-lucent central medulla and a denser cortex. The homogenously electron-dense nucleus is pointed anteriorly and is generally cylindrical, although posteriorly there is a lateral invagination that extends part-way along the nucleus. This invagination houses fine granular material of the centriolar adjunct. Vesicle-like elements that are associated with both the posterior nucleus and the centriolar adjunct are also found within the invagination. Immediately posterior of and adjoining the centriolar adjunct is a pair of mitochondrial derivatives that are elongated and extend for almost the entire length of the tail. The absence of accessory bodies in cicada sperm suggests that within the Cicadomorpha, the families Cicadidae and Cercopidae are closely affiliated.
- Full Text:
- Date Issued: 2005
- Authors: Chawanji, A S , Hodgson, Alan N , Villet, Martin H
- Date: 2005
- Language: English
- Type: Article
- Identifier: vital:6917 , http://hdl.handle.net/10962/d1011880
- Description: Mature spermatozoa from four species of platypleurine cicadas (Albanycada albigera, Azanicada zuluensis, Platypleura capensis and P. hirtipennis) were examined by light and electron microscopy. The filiform sperm have a similar ultrastructure in all species but notable variations were found in sperm dimensions. All species produce more than one discrete length of nucleated, motile sperm, a form of polymorphism termed polymegaly. Polymegaly is expressed in two ways: sperm have bi- or trimodal head and tail lengths. The anterior parts of sperm heads are embedded in an elongate homogenous matrix forming a spermatodesm. The conical acrosome is deeply invaginated posteriorly, and sits on top of the nucleus. The acrosomal contents are differentiated internally with an electron-lucent central medulla and a denser cortex. The homogenously electron-dense nucleus is pointed anteriorly and is generally cylindrical, although posteriorly there is a lateral invagination that extends part-way along the nucleus. This invagination houses fine granular material of the centriolar adjunct. Vesicle-like elements that are associated with both the posterior nucleus and the centriolar adjunct are also found within the invagination. Immediately posterior of and adjoining the centriolar adjunct is a pair of mitochondrial derivatives that are elongated and extend for almost the entire length of the tail. The absence of accessory bodies in cicada sperm suggests that within the Cicadomorpha, the families Cicadidae and Cercopidae are closely affiliated.
- Full Text:
- Date Issued: 2005
The biological control of Egeria densa Planch. (Hydrocharitaceae) in South Africa
- Authors: Smith, Rosali
- Date: 2021-10-29
- Subjects: Egeria (Plant genus) Biological control South Africa , Hydrocharitaceae Biological control South Africa , Aquatic weeds Biological control South Africa , Leafminers South Africa , Plant invasions South Africa , Resilience (Ecology) South Africa , Freshwater ecology South Africa , Hydrellia South Africa , Submerged macrophyte
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191102 , vital:45060 , 10.21504/10962/191102
- Description: Over the last thirty years, biological control, the use of host-specific natural enemies, has been a huge asset in the management exotic aquatic macrophytes such as Pistia stratiotes L. (Araceae), Pontederia crassipes Mart. (Solms) (Pontederiaceae), Azolla filiculoides Lam. (Azollaceae), Salvinia molesta D.S. Mitch (Salviniaceae) and Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae), also known as the “Big Bad Five” in South Africa. Despite these successes, freshwater ecosystems in South Africa have been harder to restore to an invasive macrophyte-free space, due to chronic disturbances such eutrophication, propagule dispersal and hydrological alterations. In the Anthropocene, where human activities have profound effects on their environment, these disturbances weakens ecological resilience and drive aquatic plant invasions. Due to long periods of invasions and the presence of a new suite of exotic aquatic plant propagules, native vegetation recolonization has been slow or even absent. Instead, the release of resources, such as sunlight, nutrient and space through aquatic weed management acts as a catalyst for secondary biological invasion. New invasive aquatic weeds include submerged and rooted emergent growth types, with Egeria densa Planch. (Hydrocharitaceae) the most widely distributed submerged aquatic weed in South Africa. It can quickly form dense monoculture stands that have ecological, economic and social impacts. Because of its ability to regenerate from plant fragments with double nodes, mechanical control is inappropriate. Additionally, mechanical and chemical control not only affects E. densa but have significant non-target effects. In response to its rapid spread over the last 20 years, especially following floating invasive aquatic management, a biological control programme was initiated, and in 2018, the leaf-mining fly, Hydrellia egeriae Rodrigues (Diptera: Ephydridae) was released. This was the first release of a biological control agent against E. densa in the world, and the first agent released against a submerged aquatic weed in South Africa. This thesis comprises the subsequent step of a biological control program when permission for the release of an agent have been obtained. A brief history of macrophyte invasions in South Africa’s unique freshwater systems are given in the literature review. Contributing factors to secondary invasions within the context of ecological resilience are introduced. An argument for the benefit of biological control as nuisance control is given, especially because E. densa and its natural enemy, H. egeriae is the focus species of this thesis. The main goal after permission for the release of an agent have been obtained, is to establish and build-up field populations. Research questions in this thesis aimed to investigate factors that contribute to or negate this goal. Through laboratory and field experiments we investigated the thermal physiology of the agent, and its climatic suitability to its novel range; different release strategies on field establishment and biotic resistance through the acquisition of novel parasitoids. Considering the longevity of this biological control program, we investigated the effects of elevated CO2 on the interaction between E. densa and H. egeriae through open top chamber experiments. Laboratory thermal physiology results showed that the agent is able to survive, develop and proliferate at all E. densa sites throughout the year. This is confirmed with the establishment of the agent at two release sites, the Nahoon River in the Eastern Cape Province and the Midmar Dam in KwaZulu-Natal. Post-release surveys showed that H. egeriae requires augmentative releases to sustain field populations. Without augmentative releases, H. egeriae herbivory levels were almost negligent. However, a contributing factor to low field-populations was parasitism. The biological control agent acquired three parasitoids, which have previously been described from Hydrellia lagarosiphon Deeming (Diptera: Ephydridae), a specific herbivore to Lagarosiphon major (Ridl.) Moss (Hydrocharitaceae). These results provide information on the immediate establishment and effectiveness of the H. egeriae. Results from the elevated CO2 study suggest that E. densa will become less nutritious through a shift in leaf C/N ratio, when ambient 800ppm is bubbled into experimental growth chambers. Hydrellia egeriae feeding was affected by ambient CO2 levels and plant nutrient availability. The set levels of ambient CO2 levels used in this experiment produced dissolved inorganic carbon levels that were lower than dissolved inorganic carbon levels in E. densa invaded sites. This suggests that, submerged aquatic plant-insect interactions may be harder to predict from only laboratory experiments. Further investigations are necessary to establish system-specific characteristics i.e. dissolved inorganic carbon and target plant nutritional quality. The biological control of E. densa in South Africa is still in its infancy. This study presents results from post-release surveys up until two years after the agent was released. From this study, Hydrellia egeriae exhibits the potential to be an effective biological control agent, but release strategies should be adapted to sustain field populations and to limit field parasitism effects. Continued post-release surveys will provide a more comprehensive idea of the seasonal fluctuations of field-populations and parasitism. Surveys at multiple sites will provide information on potential site specific characteristics that contribute to or negate biological effort. Considering the high nutrient status of South African freshwater systems, a more holistic approach to E. densa management is necessary. This will require the strengthening of ecological resilience to prevent systems from shifting into an alternate invasive stable state. In addition, aquatic weed management needs to be addressed by a resilient social network, which ultimately calls for the strengthening of socio-ecological resilience. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10-29
- Authors: Smith, Rosali
- Date: 2021-10-29
- Subjects: Egeria (Plant genus) Biological control South Africa , Hydrocharitaceae Biological control South Africa , Aquatic weeds Biological control South Africa , Leafminers South Africa , Plant invasions South Africa , Resilience (Ecology) South Africa , Freshwater ecology South Africa , Hydrellia South Africa , Submerged macrophyte
- Language: English
- Type: Doctoral theses , text
- Identifier: http://hdl.handle.net/10962/191102 , vital:45060 , 10.21504/10962/191102
- Description: Over the last thirty years, biological control, the use of host-specific natural enemies, has been a huge asset in the management exotic aquatic macrophytes such as Pistia stratiotes L. (Araceae), Pontederia crassipes Mart. (Solms) (Pontederiaceae), Azolla filiculoides Lam. (Azollaceae), Salvinia molesta D.S. Mitch (Salviniaceae) and Myriophyllum aquaticum (Vell.) Verdc. (Haloragaceae), also known as the “Big Bad Five” in South Africa. Despite these successes, freshwater ecosystems in South Africa have been harder to restore to an invasive macrophyte-free space, due to chronic disturbances such eutrophication, propagule dispersal and hydrological alterations. In the Anthropocene, where human activities have profound effects on their environment, these disturbances weakens ecological resilience and drive aquatic plant invasions. Due to long periods of invasions and the presence of a new suite of exotic aquatic plant propagules, native vegetation recolonization has been slow or even absent. Instead, the release of resources, such as sunlight, nutrient and space through aquatic weed management acts as a catalyst for secondary biological invasion. New invasive aquatic weeds include submerged and rooted emergent growth types, with Egeria densa Planch. (Hydrocharitaceae) the most widely distributed submerged aquatic weed in South Africa. It can quickly form dense monoculture stands that have ecological, economic and social impacts. Because of its ability to regenerate from plant fragments with double nodes, mechanical control is inappropriate. Additionally, mechanical and chemical control not only affects E. densa but have significant non-target effects. In response to its rapid spread over the last 20 years, especially following floating invasive aquatic management, a biological control programme was initiated, and in 2018, the leaf-mining fly, Hydrellia egeriae Rodrigues (Diptera: Ephydridae) was released. This was the first release of a biological control agent against E. densa in the world, and the first agent released against a submerged aquatic weed in South Africa. This thesis comprises the subsequent step of a biological control program when permission for the release of an agent have been obtained. A brief history of macrophyte invasions in South Africa’s unique freshwater systems are given in the literature review. Contributing factors to secondary invasions within the context of ecological resilience are introduced. An argument for the benefit of biological control as nuisance control is given, especially because E. densa and its natural enemy, H. egeriae is the focus species of this thesis. The main goal after permission for the release of an agent have been obtained, is to establish and build-up field populations. Research questions in this thesis aimed to investigate factors that contribute to or negate this goal. Through laboratory and field experiments we investigated the thermal physiology of the agent, and its climatic suitability to its novel range; different release strategies on field establishment and biotic resistance through the acquisition of novel parasitoids. Considering the longevity of this biological control program, we investigated the effects of elevated CO2 on the interaction between E. densa and H. egeriae through open top chamber experiments. Laboratory thermal physiology results showed that the agent is able to survive, develop and proliferate at all E. densa sites throughout the year. This is confirmed with the establishment of the agent at two release sites, the Nahoon River in the Eastern Cape Province and the Midmar Dam in KwaZulu-Natal. Post-release surveys showed that H. egeriae requires augmentative releases to sustain field populations. Without augmentative releases, H. egeriae herbivory levels were almost negligent. However, a contributing factor to low field-populations was parasitism. The biological control agent acquired three parasitoids, which have previously been described from Hydrellia lagarosiphon Deeming (Diptera: Ephydridae), a specific herbivore to Lagarosiphon major (Ridl.) Moss (Hydrocharitaceae). These results provide information on the immediate establishment and effectiveness of the H. egeriae. Results from the elevated CO2 study suggest that E. densa will become less nutritious through a shift in leaf C/N ratio, when ambient 800ppm is bubbled into experimental growth chambers. Hydrellia egeriae feeding was affected by ambient CO2 levels and plant nutrient availability. The set levels of ambient CO2 levels used in this experiment produced dissolved inorganic carbon levels that were lower than dissolved inorganic carbon levels in E. densa invaded sites. This suggests that, submerged aquatic plant-insect interactions may be harder to predict from only laboratory experiments. Further investigations are necessary to establish system-specific characteristics i.e. dissolved inorganic carbon and target plant nutritional quality. The biological control of E. densa in South Africa is still in its infancy. This study presents results from post-release surveys up until two years after the agent was released. From this study, Hydrellia egeriae exhibits the potential to be an effective biological control agent, but release strategies should be adapted to sustain field populations and to limit field parasitism effects. Continued post-release surveys will provide a more comprehensive idea of the seasonal fluctuations of field-populations and parasitism. Surveys at multiple sites will provide information on potential site specific characteristics that contribute to or negate biological effort. Considering the high nutrient status of South African freshwater systems, a more holistic approach to E. densa management is necessary. This will require the strengthening of ecological resilience to prevent systems from shifting into an alternate invasive stable state. In addition, aquatic weed management needs to be addressed by a resilient social network, which ultimately calls for the strengthening of socio-ecological resilience. , Thesis (PhD) -- Faculty of Science, Zoology and Entomology, 2021
- Full Text:
- Date Issued: 2021-10-29
Rhodes University Graduation Ceremony 1989
- Authors: Rhodes University
- Date: 1989
- Language: English
- Type: text
- Identifier: vital:8123 , http://hdl.handle.net/10962/d1005706
- Description: Rhodes University Graduation Ceremonies on Friday, 7 April 1989 at 8 p.m. [and] on Saturday, 8 April 1989 at 10 a.m. in the 1820 Settlers National Monument. , Rhodes University East London Graduation Ceremony Saturday; 13 May 1989 at 11.30 a.m. in the Guild Theatre.
- Full Text:
- Date Issued: 1989
- Authors: Rhodes University
- Date: 1989
- Language: English
- Type: text
- Identifier: vital:8123 , http://hdl.handle.net/10962/d1005706
- Description: Rhodes University Graduation Ceremonies on Friday, 7 April 1989 at 8 p.m. [and] on Saturday, 8 April 1989 at 10 a.m. in the 1820 Settlers National Monument. , Rhodes University East London Graduation Ceremony Saturday; 13 May 1989 at 11.30 a.m. in the Guild Theatre.
- Full Text:
- Date Issued: 1989
Endothermy and chorusing behaviour in the African platypleurine cicada Pycna semiclara (Germar, 1834) (Hemiptera: Cicadidae)
- Villet, Martin H, Sanborn, Allen F, Phillips, P K
- Authors: Villet, Martin H , Sanborn, Allen F , Phillips, P K
- Date: 2003
- Language: English
- Type: text , Article
- Identifier: vital:6892 , http://hdl.handle.net/10962/d1011652 , http://dx.doi.org/10.1139/z03-119
- Description: Cicadas use acoustic signals to find mates and therefore offer a phylogenetically independent opportunity to test the generality of ideas about acoustic communication that were developed from studies of other animals. Pycna semiclara (Germar, 1834) (Hemiptera: Cicadidae) is a forest-dwelling platypleurine cicada that uses its calling song to form choruses and attract mates. Additionally, P. semiclara produces an encounter call that is involved in courtship and also in spacing males within choruses. Males generally call from exposed trunks and branches within the understory but clear of the undergrowth and fight with other males that call within about 50 cm of them. Choruses sing sporadically throughout the day but focus most of their calling activity into half-hour bouts at dawn and dusk. Body size and ambient temperature had no significant effect on spectral or temporal characteristics of the calling song. Body temperature measurements indicate that P. semiclara thermoregulates endothermically, with a body temperature of more than 22 °C above ambient temperature being measured during calling activity at dusk. Such endothermy provides an advantage to the cicadas by allowing them to call during crepuscular hours when atmospheric conditions are most optimal for acoustic communication and predation risks are minimal. Coincidentally, endogenously regulating body temperature allows the temporal characteristics of the call to be unaffected by ambient temperature changes.
- Full Text:
- Date Issued: 2003
- Authors: Villet, Martin H , Sanborn, Allen F , Phillips, P K
- Date: 2003
- Language: English
- Type: text , Article
- Identifier: vital:6892 , http://hdl.handle.net/10962/d1011652 , http://dx.doi.org/10.1139/z03-119
- Description: Cicadas use acoustic signals to find mates and therefore offer a phylogenetically independent opportunity to test the generality of ideas about acoustic communication that were developed from studies of other animals. Pycna semiclara (Germar, 1834) (Hemiptera: Cicadidae) is a forest-dwelling platypleurine cicada that uses its calling song to form choruses and attract mates. Additionally, P. semiclara produces an encounter call that is involved in courtship and also in spacing males within choruses. Males generally call from exposed trunks and branches within the understory but clear of the undergrowth and fight with other males that call within about 50 cm of them. Choruses sing sporadically throughout the day but focus most of their calling activity into half-hour bouts at dawn and dusk. Body size and ambient temperature had no significant effect on spectral or temporal characteristics of the calling song. Body temperature measurements indicate that P. semiclara thermoregulates endothermically, with a body temperature of more than 22 °C above ambient temperature being measured during calling activity at dusk. Such endothermy provides an advantage to the cicadas by allowing them to call during crepuscular hours when atmospheric conditions are most optimal for acoustic communication and predation risks are minimal. Coincidentally, endogenously regulating body temperature allows the temporal characteristics of the call to be unaffected by ambient temperature changes.
- Full Text:
- Date Issued: 2003
Atu pandula Tate Nampongo
- 2 Men and 3 Ladies, Ovambo Folk, Simon, Kornelia, Dargie, Dave
- Authors: 2 Men and 3 Ladies , Ovambo Folk , Simon, Kornelia , Dargie, Dave
- Date: 1982-11-02
- Subjects: Choral music , Field recordings , Africa, Sub-Saharan , Africa Namibia Oshikuku f-sx
- Language: Kuanyama, Kwanyama
- Type: sound recordings , field recordings , sound recording-musical
- Identifier: http://hdl.handle.net/10962/279026 , vital:55456 , International Library of African Music, Rhodes University, Makhanda, South Africa , Dave Dargie Field Tapes, Rhodes University, Makhanda, South Africa , DDD058-07
- Description: Indigenous music.
- Full Text: false
- Date Issued: 1982-11-02
- Authors: 2 Men and 3 Ladies , Ovambo Folk , Simon, Kornelia , Dargie, Dave
- Date: 1982-11-02
- Subjects: Choral music , Field recordings , Africa, Sub-Saharan , Africa Namibia Oshikuku f-sx
- Language: Kuanyama, Kwanyama
- Type: sound recordings , field recordings , sound recording-musical
- Identifier: http://hdl.handle.net/10962/279026 , vital:55456 , International Library of African Music, Rhodes University, Makhanda, South Africa , Dave Dargie Field Tapes, Rhodes University, Makhanda, South Africa , DDD058-07
- Description: Indigenous music.
- Full Text: false
- Date Issued: 1982-11-02
Historical biogeography of the tribe Platypleurini Schmidt, 1918 (Hemiptera: Cicadidae) with a focus on Southern Africa
- Authors: Price, Benjamin Wills
- Date: 2010
- Subjects: Biogeography -- History -- Africa, Southern Cicadas -- Africa, Southern Cicada (Genus) -- Africa, Southern Biodiversity -- Africa, Southern Cicadas -- Variation -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5708 , http://hdl.handle.net/10962/d1005394
- Description: With our contemporary biota under increasing threat of extinction, it is of interest to understand where, why and how biological diversity is generated. If focussed on appropriate taxa, phylogeographic and phylogenetic studies can assist in the identification of both places and processes central to the origin and maintenance of biological diversity. It is explained why southern Africa presents a perfect test-bed for exploring such mechanisms of diversification and why cicadas (Hemiptera: Cicadidae) have proved very suitable tools for studies of historical biogeography. This study then exemplifies these points by providing the first large-scale investigation of the historical biogeography of the tribe Platypleurini Schmidt, 1918, with emphasis on the genus Platypleura Amyot & Seville, 1843 in southern Africa. Standard methods of DNA sequencing provided data from portions of the mitochondrial small subunit ribosomal 16S RNA (16S) and cytochrome oxidase subunits I (COI) and II (COII); and the nuclear elongation factor 1 alpha (EF-1α) from 400 ethanol-preserved specimens. These data were analysed using standard phylogenetic methods and a time scale of diversification was estimated using a Bayesian framework and both fossil data and DNA substitution rates. The results showed that the tribe is too recent to be of Gondwanan origin. The lack of monophyly of the genera represented in both Asia and Africa showed that the tribe needs formal taxonomic revision. Diversification of the African platypleurine genera coincides with aridification in the early Oligocene. Dispersal of Asian platypleurine taxa coincides with the meeting of Africa and Eurasia in the mid-Oligocene. Two radiations within African Platypleura are hypothesised; one distributed over most of sub-Saharan Africa and the second restricted to southern Africa, with clades restricted within regional biomes. Within each of the three focal biomes, cryptic taxonomic diversity was confirmed, suggesting that, even in relatively well understood groups such as the southern African platypleurine cicadas, molecular data can identify further diversity. Although each focal taxon was restricted to non-overlapping biomes, comparison of the three biomes highlighted interactions between palaeoclimates and fixed landscape features (coastal topography, river catchments and escarpments) as causative agents of vicariance, dispersal, extinction and diversification of these volant insects. The results of using co-distributed species for comparative study cautions against making inferences based on single-taxon datasets and highlights the need to use many, evolutionarily independent taxa when identifying mechanisms of diversification. The dating analyses imply that within-species lineage diversification occurred overwhelmingly within the Pleistocene, a trend that is being increasingly recognised in print for other biota. Some caveats about using phylogenetic approaches to estimate ancestral areas are illustrated. Several recommendations are made regarding additional taxa and data sources for understanding the origin and maintenance of biological diversity.
- Full Text:
- Date Issued: 2010
- Authors: Price, Benjamin Wills
- Date: 2010
- Subjects: Biogeography -- History -- Africa, Southern Cicadas -- Africa, Southern Cicada (Genus) -- Africa, Southern Biodiversity -- Africa, Southern Cicadas -- Variation -- Africa, Southern
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5708 , http://hdl.handle.net/10962/d1005394
- Description: With our contemporary biota under increasing threat of extinction, it is of interest to understand where, why and how biological diversity is generated. If focussed on appropriate taxa, phylogeographic and phylogenetic studies can assist in the identification of both places and processes central to the origin and maintenance of biological diversity. It is explained why southern Africa presents a perfect test-bed for exploring such mechanisms of diversification and why cicadas (Hemiptera: Cicadidae) have proved very suitable tools for studies of historical biogeography. This study then exemplifies these points by providing the first large-scale investigation of the historical biogeography of the tribe Platypleurini Schmidt, 1918, with emphasis on the genus Platypleura Amyot & Seville, 1843 in southern Africa. Standard methods of DNA sequencing provided data from portions of the mitochondrial small subunit ribosomal 16S RNA (16S) and cytochrome oxidase subunits I (COI) and II (COII); and the nuclear elongation factor 1 alpha (EF-1α) from 400 ethanol-preserved specimens. These data were analysed using standard phylogenetic methods and a time scale of diversification was estimated using a Bayesian framework and both fossil data and DNA substitution rates. The results showed that the tribe is too recent to be of Gondwanan origin. The lack of monophyly of the genera represented in both Asia and Africa showed that the tribe needs formal taxonomic revision. Diversification of the African platypleurine genera coincides with aridification in the early Oligocene. Dispersal of Asian platypleurine taxa coincides with the meeting of Africa and Eurasia in the mid-Oligocene. Two radiations within African Platypleura are hypothesised; one distributed over most of sub-Saharan Africa and the second restricted to southern Africa, with clades restricted within regional biomes. Within each of the three focal biomes, cryptic taxonomic diversity was confirmed, suggesting that, even in relatively well understood groups such as the southern African platypleurine cicadas, molecular data can identify further diversity. Although each focal taxon was restricted to non-overlapping biomes, comparison of the three biomes highlighted interactions between palaeoclimates and fixed landscape features (coastal topography, river catchments and escarpments) as causative agents of vicariance, dispersal, extinction and diversification of these volant insects. The results of using co-distributed species for comparative study cautions against making inferences based on single-taxon datasets and highlights the need to use many, evolutionarily independent taxa when identifying mechanisms of diversification. The dating analyses imply that within-species lineage diversification occurred overwhelmingly within the Pleistocene, a trend that is being increasingly recognised in print for other biota. Some caveats about using phylogenetic approaches to estimate ancestral areas are illustrated. Several recommendations are made regarding additional taxa and data sources for understanding the origin and maintenance of biological diversity.
- Full Text:
- Date Issued: 2010
Mechanisms generating biological diversity in the genus Platypleura Amyot & Serville, 1843 (Hemiptera: Cicadidae) in southern Africa: implications of a preliminary molecular phylogeny
- Villet, Martin He, Barker, Nigel P, Lunt, N
- Authors: Villet, Martin He , Barker, Nigel P , Lunt, N
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6554 , http://hdl.handle.net/10962/d1006012
- Description: Truly understanding biological diversity requires a move from descriptive studies to mechanistic interpretations based on comparative biology and a thorough recognition of the natural history of the focal organisms. A useful step in such comparative studies is the generation of a phylogeny, so that one can assess the phylogenetic independence of the focal taxa and trace the evolutionary significance of their characteristics. As a preliminary to such studies on the platypleurine cicada genus Platypleura, we sequenced 498 bases of the cytochrome oxidase I (COI) gene from thirteen African species. To circumvent problems with outgroup selection, we also included sequences from representatives of the platypleurine genera Brevisiana, Capcicada, Munza, Oxypleura, Severiana, and Systophlochius, all of the subtribe Platypleuriti, and two species of the genus Ugada, of the subtribe Hainanosemiiti. The resulting phylogenies support the synonymization of the monotypic genus Systophlochius with the widespread, speciose genus Platypleura; confirm the placement of Platypleura sp. 7 in that genus; and confirm the independence of Capcicada and Platypleura. Although the preliminary phylogeny lacks strong support at many nodes, it suggests that three radiations of Platypleura have occurred in southern Africa and that there was progressive southward speciation of these radiations. A novel modification of the ancestral area analysis further suggests that the group has an ancestral association with acacias but there were five independent speciation events associated with host- switching. These insights can be summarized by a general hypothesis that the mechanisms underlying platypleurine biodiversity in southern Africa involve two ancient vicariance events and subsequent speciation by vicariance, switching of plant associations, and changes of habitat preferences. We offer this example to illustrate how analysis of preliminary data can help to generate hypotheticodeductive research hypotheses, to provoke interest in testing these hypotheses, and to illustrate the utility of phylogenies beyond systematics.
- Full Text:
- Date Issued: 2004
- Authors: Villet, Martin He , Barker, Nigel P , Lunt, N
- Date: 2004
- Language: English
- Type: Article
- Identifier: vital:6554 , http://hdl.handle.net/10962/d1006012
- Description: Truly understanding biological diversity requires a move from descriptive studies to mechanistic interpretations based on comparative biology and a thorough recognition of the natural history of the focal organisms. A useful step in such comparative studies is the generation of a phylogeny, so that one can assess the phylogenetic independence of the focal taxa and trace the evolutionary significance of their characteristics. As a preliminary to such studies on the platypleurine cicada genus Platypleura, we sequenced 498 bases of the cytochrome oxidase I (COI) gene from thirteen African species. To circumvent problems with outgroup selection, we also included sequences from representatives of the platypleurine genera Brevisiana, Capcicada, Munza, Oxypleura, Severiana, and Systophlochius, all of the subtribe Platypleuriti, and two species of the genus Ugada, of the subtribe Hainanosemiiti. The resulting phylogenies support the synonymization of the monotypic genus Systophlochius with the widespread, speciose genus Platypleura; confirm the placement of Platypleura sp. 7 in that genus; and confirm the independence of Capcicada and Platypleura. Although the preliminary phylogeny lacks strong support at many nodes, it suggests that three radiations of Platypleura have occurred in southern Africa and that there was progressive southward speciation of these radiations. A novel modification of the ancestral area analysis further suggests that the group has an ancestral association with acacias but there were five independent speciation events associated with host- switching. These insights can be summarized by a general hypothesis that the mechanisms underlying platypleurine biodiversity in southern Africa involve two ancient vicariance events and subsequent speciation by vicariance, switching of plant associations, and changes of habitat preferences. We offer this example to illustrate how analysis of preliminary data can help to generate hypotheticodeductive research hypotheses, to provoke interest in testing these hypotheses, and to illustrate the utility of phylogenies beyond systematics.
- Full Text:
- Date Issued: 2004
Polymorphism and fighting in male fig wasps
- Authors: Vincent, Stephanie Louise
- Date: 1992
- Subjects: Fig wasp Chalcid wasps -- Morphology Wasps
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5740 , http://hdl.handle.net/10962/d1005426
- Description: Male fig wasps (Hymenoptera: Chalcidoidea) exhibit a fascinating range of morphology and behaviour. A cluster analysis, based on descriptions of the males of several hundred species, distinguished six major morphological groups. Behaviourial observations suggest that male morphology is related to the levels of inter-male aggression. Three behaviourial groupings were identified. Fighting species generally mated in the fig cavity, pacifist species mated in the females' galls or outside the figs. Mating sites are thus the primary determinants of male morphology and behaviour. In fighting species males were larger than their females, whereas pacifists and aggressors were equal in size or smaller than conspecific females. The large males in fighting fig wasps appear to be a consequence of sexual selection because larger males tended to win fights. Within a species there were no differences in the size of the galls that produced males and females, even in species where sexual size differences were present, suggesting that there is a heritable component to wasp size. No alternative advantages for smaller males were detected. Although fights were sometimes fatal, damage was not always a consequence of fighting behaviour and was recorded in both fighting and pacifist species. Sex ratios in several species were more female biased at higher population densities. Sex ratios of species with 'internally' ovipositing species were heavily female biased, but approached 1:1 in more outbred species with 'externally' ovipositing females. Levels of matedness, among females ranged from 73% to 99%. No evidence for sperm exhaustion was obtained. Species of Philotrypesis with both winged and flightless males were present only in southern African Ficus species from subsections Platyphyllae and Chlamydodorae. No species had only winged males. The flightless males of some Philotrypesis species were themselves polymorphic. In one polymorphic Philotrypesis species, winged males were found to be rare at high densities, but common at low densities. Digitata and religiosa males of Otitesella differed in coloration, size and behaviour. Digitata males were aggressors while religiosa males were fighters. Digitata males escaped from the figs whereas religiosa males remained inside the figs, perhaps because only digitata males were attracted to Light. Proportionally more digitata than religiosa males were present in low density populations and females were found to respond differently to the two morphs.
- Full Text:
- Date Issued: 1992
- Authors: Vincent, Stephanie Louise
- Date: 1992
- Subjects: Fig wasp Chalcid wasps -- Morphology Wasps
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:5740 , http://hdl.handle.net/10962/d1005426
- Description: Male fig wasps (Hymenoptera: Chalcidoidea) exhibit a fascinating range of morphology and behaviour. A cluster analysis, based on descriptions of the males of several hundred species, distinguished six major morphological groups. Behaviourial observations suggest that male morphology is related to the levels of inter-male aggression. Three behaviourial groupings were identified. Fighting species generally mated in the fig cavity, pacifist species mated in the females' galls or outside the figs. Mating sites are thus the primary determinants of male morphology and behaviour. In fighting species males were larger than their females, whereas pacifists and aggressors were equal in size or smaller than conspecific females. The large males in fighting fig wasps appear to be a consequence of sexual selection because larger males tended to win fights. Within a species there were no differences in the size of the galls that produced males and females, even in species where sexual size differences were present, suggesting that there is a heritable component to wasp size. No alternative advantages for smaller males were detected. Although fights were sometimes fatal, damage was not always a consequence of fighting behaviour and was recorded in both fighting and pacifist species. Sex ratios in several species were more female biased at higher population densities. Sex ratios of species with 'internally' ovipositing species were heavily female biased, but approached 1:1 in more outbred species with 'externally' ovipositing females. Levels of matedness, among females ranged from 73% to 99%. No evidence for sperm exhaustion was obtained. Species of Philotrypesis with both winged and flightless males were present only in southern African Ficus species from subsections Platyphyllae and Chlamydodorae. No species had only winged males. The flightless males of some Philotrypesis species were themselves polymorphic. In one polymorphic Philotrypesis species, winged males were found to be rare at high densities, but common at low densities. Digitata and religiosa males of Otitesella differed in coloration, size and behaviour. Digitata males were aggressors while religiosa males were fighters. Digitata males escaped from the figs whereas religiosa males remained inside the figs, perhaps because only digitata males were attracted to Light. Proportionally more digitata than religiosa males were present in low density populations and females were found to respond differently to the two morphs.
- Full Text:
- Date Issued: 1992
Predicting geographic distribution of seven blowfly species (Diptera: Calliphoridae) in South Africa
- Richards, C S, Williams, K A, Villet, Martin H
- Authors: Richards, C S , Williams, K A , Villet, Martin H
- Date: 2009
- Language: English
- Type: text , Article
- Identifier: vital:6854 , http://hdl.handle.net/10962/d1011135
- Description: The predicted geographic distributions of seven forensically important blowfly species are modelled using the computer program Maxent, based on selected climatic variables for South Africa, a country with large climatic and environmental gradients. It is shown that although temperature was hypothesized to most influence the distributions of these ectotherms, moisture, and particularly humidity, was in fact usually paramount. Chrysomya albiceps (Wiedemann) and C. marginalis (Robineau-Desvoidy) had the most widespread geographic and climatic distribution, while the forest-associated C. inclinata(Walker) was the least widespread. Chrysomya putoria (Wiedemann) and C. megacephala (Fabricius) had very similar predicted distributions that were restricted mainly to Limpopo, Mpumalanga, KwaZulu-Natal and the coast of the Eastern Cape. Chrysomya chloropyga (Wiedemann) and Calliphora croceipalpis (Jaennicke) were the only species predicted to occur at high altitudes. Blowfly distributions restricted to part of the map area were predicted better than those that were more widespread in the region, presumably because species with extremely widespread distributions in a study area occupy nearly the whole range of variation of most predictor variables, leaving little variation with which themaximumentropy modelling method can discriminate between presence and absence of the organism.
- Full Text:
- Date Issued: 2009
Predicting geographic distribution of seven blowfly species (Diptera: Calliphoridae) in South Africa
- Authors: Richards, C S , Williams, K A , Villet, Martin H
- Date: 2009
- Language: English
- Type: text , Article
- Identifier: vital:6854 , http://hdl.handle.net/10962/d1011135
- Description: The predicted geographic distributions of seven forensically important blowfly species are modelled using the computer program Maxent, based on selected climatic variables for South Africa, a country with large climatic and environmental gradients. It is shown that although temperature was hypothesized to most influence the distributions of these ectotherms, moisture, and particularly humidity, was in fact usually paramount. Chrysomya albiceps (Wiedemann) and C. marginalis (Robineau-Desvoidy) had the most widespread geographic and climatic distribution, while the forest-associated C. inclinata(Walker) was the least widespread. Chrysomya putoria (Wiedemann) and C. megacephala (Fabricius) had very similar predicted distributions that were restricted mainly to Limpopo, Mpumalanga, KwaZulu-Natal and the coast of the Eastern Cape. Chrysomya chloropyga (Wiedemann) and Calliphora croceipalpis (Jaennicke) were the only species predicted to occur at high altitudes. Blowfly distributions restricted to part of the map area were predicted better than those that were more widespread in the region, presumably because species with extremely widespread distributions in a study area occupy nearly the whole range of variation of most predictor variables, leaving little variation with which themaximumentropy modelling method can discriminate between presence and absence of the organism.
- Full Text:
- Date Issued: 2009