Plastochron index - an indicator of plant structure and function a case study using Pisum sativum L
- Authors: Ade-Ademilua, Omobolanle Elizabeth
- Date: 2006
- Subjects: Plant anatomy Plant physiology Peas -- Anatomy Peas -- Physiology
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4183 , http://hdl.handle.net/10962/d1003751
- Description: The use of chronological age for example, using days after sowing (DAS), or days after germination (DAG) as a time variable may result in the inherent variability between plants resulting in differences which can be large enough to obscure subtle developmental trends that become evident among plants sown at the same time. An alternative to DAS or DAG is the plastochron index (PI), first used by Erickson and Michelini (1957) as a morphological time scale and numerical index; which to according to the authors suggested and represented a more accurate reflection of the developmental status of a plant. The research presented in this thesis was therefore aimed specifically at utilizing the index in qualitative and quantitative analyses, to confirm its usefulness in analyzing and predicting plant growth and development. Specifically this research focused on investigating various morphological and physiological events that together, hopefully, would serve as a template for the prediction of the growth, development and reactions of Pisum sativum L. to different growth conditions. In Chapter 3, the use of the average length of the first pair of leaflets on each node as a suitable parameter for calculating PI in P. sativum is suggested. The results presented in Chapter 3 suggest that plant age is best expressed using the plastochron index, as this reflects the time interval between the initiations of successive pairs of leaflets. This section of the research has been published as “Ade-Ademilua OE, Botha CEJ (2005) A re-evaluation of plastochron index in peas - a case for using leaflet length. South African Journal of Botany 71: 76-80”. The PI formula developed was subsequently used in this research to conduct qualitative and quantitative investigations of plant growth and development in which all data and observations were related directly to the plastochron index. In Chapter 4, the sink to source transition in Pisum sativum L. leaves at different plastochron ages in nodulating plants was investigated using the phloem-mobile fluorescent marker, 5,6-carboxyfluorescein (5,6-CF). The results demonstrated that young leaves remained strong sinks up until LPI 0, after which sink-source transition occurred up to LPI 1.8 and leaflets transitioned to strong source systems by LPI 2.0. A well-developed cross-connected phloem system between paired leaflets in peas, and the petiole and the stem vascular supply was observed. The data presented in the second part of Chapter 4 suggest that the phloem transport between leaflet pairs is independent of the sink/source state of the leaflets, or of movement along the source to sink gradient. The data support the presence of a modular transport system which may ensure re-allocation and balancing between leaflets of the same physiological age and photosynthetic and transport status, thereby load-balancing the local transport system, before exporting to other younger (sink) regions. The investigation of leaf development using the plastochron index (Chapter 5) revealed that the formation of air spaces in the palisade and spongy mesophyll, one of the preparatory events for transition from sink to source state in developing leaves, occurs between LPI 0 and LPI 1 in pea leaflets. Results of the anatomical and ultrastructural study related to PI are presented in Chapter 5. The density of wall ingrowths in transfer cells of minor veins increased with LPI and appeared to be associated with the probable transition to source state and the related potential increase in the production of assimilates for export. The onset of wall ingrowth development in leaflets at LPI 0 provided evidence that sink-to-source transition commences at LPI 0 in P. sativum. Presumably-functional plasmodesmata as well as a few mature sieve elements were evident in class IV veins in the apical region of young and older leaflets at LPI 0. The number of mature sieve elements per vein however, increased with increasing LPI. Most class V veins were still undergoing division at LPI 0 and their sieve elements did not show signs of maturity until LPI 1. The increase in the number of mature metaphloem sieve elements in young, supposedly importing tissue at LPI 0 to older, supposedly exporting tissues at LPI 2 is evidence of the association between phloem maturation and transition from importing to exporting status. In Chapter 6, I report on the effects of elevated CO[subscript 2] on the growth and leaf development of nodulating and non-nodulating Pisum sativum L var. Greenfeast grown under controlled environment of the same nitrogen (6mM) and nitrogen- free nutrient solution conditions. Shortterm exposure to elevated CO[subscript 2] induced rapid plant growth, irrespective of treatment. However, long-term elevated CO[subscript 2] treatment did not affect rate of leaf appearance (RLA) in nodulated plants, irrespective of mineral N supply but enhanced RLA in non- nodulating plants supplied with mineral N. Supplied N resulted in a significant increase in leaflet elongation rate (LfER) under both ambient and elevated CO[subscript 2], but LfER was not significantly affected by nodulation but was increased by high CO[subscript 2]. This suggested that the growth of nodulating P. sativum L may not be significantly affected under CO[subscript 2] levels as high as 1000 μmol mol[superscript -1]. The data suggest that elevated CO[subscript 2] will enhance canopy size, provided adequate soil N is available and more so in non-nodulating plants. This section of the research has been published as “Ade-Ademilua OE, Botha CEJ (2004) The effects of elevated CO[subscript 2] and nitrogen availability supersedes the need for nodulation in peas grown under controlled environmental conditions. South African Journal of Botany 70: 816 – 823”. This thesis demonstrates that the similarity in the qualitative analyses results obtained from plants from different CO[subscript 2], nitrogen and nodulation treatment conditions, highlights the fact that plants of same PI value are at the same developmental state, irrespective of the growth condition. Furthermore, changes in plant structure and function observed under different growth conditions can be related simply to changes in plastochron index. The work presented in this thesis demonstrate that changes in plant structure and function analyzed are related to changes in PI. An important finding of this thesis is that with the use of PI, results can be compiled as a template for predicting the structure- function state of pea plants at any plastochron age, under any growth conditions, before using small representative sample populations.
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- Date Issued: 2006
A taxonomic revision of the southern African endemic genus Gazania (Asteraceae) based on morphometric, genetic and phylogeographic data
- Authors: Howis, Seranne
- Date: 2007
- Subjects: Compositae Plant genetics DNA Endemic plants -- South Africa Plant ecology -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4200 , http://hdl.handle.net/10962/d1003769
- Description: Gazania is a small genus of the subtribe Gorteriinae, tribe Arctoteae, that is endemic to southern Africa. The genus was last revised in 1959 by Roessler, who noted that delimitation of the species of Gazania can be “extraordinarily difficult”. Morphometric data was collected to test the reality of the 16 species as delimited by Roessler, who based species boundaries on morphological characters. Only six taxa were found to be morphologically distinct, while the remaining samples showed no species cohesion. DNA sequence data from two nuclear spacer regions (ITS and ETS) and four chloroplast noncoding regions (the trnL and rpS16 introns, and the psbA-trnH and trnL-F spacers) of 43 samples were utilised to create a species level phylogeny and to investigate correlations between genetically delimited units and morphologically defined taxa. DNA sequence data reveal that seven species (as delimited by Roessler) are morphologically and genetically distinct. The remaining nine of Roessler’s species fall into a morphologically and genetically overlapping continuum that forms an ochlospecies. Phylogeographic methods (based on an expanded ITS and ETS DNA sequence data set from 169 samples) were employed to further resolve the limits of species, with special focus on the clades within the ochlospecies. These genetically defined clades were correlated with their geographical distributions, and in combination with molecular dating techniques, used to elucidate the recent climatic or environmental factors that may have shaped the phylogeographic structure of the genus. Phylogeographic patterns and molecular dating reveals that the genus Gazania is an example of a South African endemic clade that has undergone episodic cladogenesis in response to fluctuating climatic conditions over the last seven million years. The ochlospecies within Gazania is a result of repeated cycles of climate driven isolation in refugia and subsequent expansion and hybridization events during the Pliocene and Pleistocene. Comparisons with phylogeographic studies on other organisms reveal a common pattern indicative of the presence and evolutionary importance of an ancestral refugium in the arid Richtersveld / Namib region of southern Africa.
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- Date Issued: 2007
Evolutionary and biogeographic studies in the genus Kniphofia moench (Asphodelaceae)
- Authors: Ramdhani, Syd
- Date: 2007
- Subjects: Asphodelaceae Asphodelaceae -- Genetics Cladistic analysis
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4220 , http://hdl.handle.net/10962/d1003789
- Description: Kniphofia, a genus of approximately 71 species, is almost entirely African with two species occurring in Madagascar and one in Yemen. Commonly known as ‘red hot pokers’ they are popular among horticulturists. The genus is also well known for its complex alpha taxonomy. To date, no studies have examined the phylogenetic relationships among species or the evolutionary history of the genus, and little work has been done on their biogeography. The main focus of this study was (i) to review the alpha taxonomy, (ii) to assess diversity and endemism in Kniphofia, (iii) to use DNA sequence data to reconstruct a specieslevel phylogeny to understand intra-generic species relationships and evolutionary processes (iv) to use phylogeographic approaches to study the biogeography and evaluate biogeographical patterns, and (v) to assess anatomical variation and determine if anatomical characters are useful for species delimitation. It was found that the genus has six centres of diversity, five of which are centres of endemism. The South African Centre is the most speciose and is also the largest centre of endemism. Kniphofia shows a strong Afromontane grassland affinity in Tropical and East Africa. In South Africa, it is found from high altitudes to coastal habitats, with the most speciose regions being Afromontane grasslands. It is thus not considered to be an Afromontane element, but rather an Afromontane associate. Five major evolutionary lineages were identified using cpDNA sequence data (trnT-L spacer), four of which are southern African. The fifth lineage is represented by material from Madagascar, East and Tropical Africa. The nuclear ITS region failed to provide resolution, as many sequences were identical. The five lineages recovered using cpDNA showed some congruence with geographic origin rather than the taxonomic arrangement based on morphology. All of the species with multiple samples were non-monophyletic. This could be due to hybridisation and/or incomplete lineage sorting. The nested clade analysis, although preliminary, did not completely agree with the phylogenetic analyses. One of the three third level nested clades appears to show fragmentation between the Cape Region, KwaZulu-Natal and northern parts of southern Africa. Furthermore, another nested clades recovered suggest a range expansion and radiation from the Drakensberg into the adjacent Drakensberg-Maputoland-Pondoland transition. Morphological species of Kniphofia exhibited substantial leaf anatomical variation and anatomical characters do not cluster samples into their morphological species. The anatomical results do not fit any geographic pattern, nor do they correspond to the lineages recovered using molecular markers or the nested clades. Leaf anatomical variation does not appear to be influenced by geographical or environmental factors. However, hybridisation may play a role but was not tested in this study. In light of the above findings it is proposed that the evolutionary and biogeographic history of Kniphofia is strongly linked to tectonic events, and Quaternary climatic cycles and vegetation changes. Tectonic events (viz. uplifts) may have resulted in vicariance events that may account for the five cpDNA lineages recovered in phylogenetic analyses, while Quaternary climatic cycles and vegetation changes may have had a more recent impact on evolution and biogeography. It is hypothesised that the ancestral area for Kniphofia was much more widespread when Afromontane grasslands were more extensive during cooler and drier glacial episodes. Kniphofia on the high mountains of Tropical and East Africa would have tracked Afromontane grasslands as they expanded their ranges in cooler periods. While during wetter and warmer interglacial periods Kniphofia would have retreated into refugia on the mountains of Tropical and East Africa, with no gene flow possible between these refugia. In South Africa, where latitude compensates for altitude, Kniphofia may have maintained a distribution that extended into the lowlands even during interglacials. A cyclic climate change hypothesis implies that populations of Kniphofia (at different phases of the climatic cycle) would have experienced periods of contractions and fragmentation followed by periods of range expansion and coalescence or secondary contact. Altitudinal shifting is proposed to be the most likely mechanism for fragmentation and range expansion, and would would possibly promoted hybridisation. Within the five lineages there is evidence for recent differentiation as the branch lengths are short, there are numerous nonmonophyletic species and numerous identical haplotypes (cpDNA and ITS) which collectively indicate a recent radiation in southern Africa. A recent radiation would also account for the taxonomic confusion and difficulty in differentiating morpho-species. These climatic events may also account for the substantial anatomical variation in southern African Kniphofia species.
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- Date Issued: 2007
Investigating the effect of Glomus etunicatum colonization on structure and phloem transport in roots of Eragrostis curvula (Umgeni)
- Authors: Skinner, Amy
- Date: 2007
- Subjects: Glomus (Fungi) , Phloem , Plant translocation , Weeping lovegrass , Vesicular-arbuscular mycorrhizas , Mycorrhizal fungi , Mycorrhizas
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4227 , http://hdl.handle.net/10962/d1003796 , Glomus (Fungi) , Phloem , Plant translocation , Weeping lovegrass , Vesicular-arbuscular mycorrhizas , Mycorrhizal fungi , Mycorrhizas
- Description: The symbiotic unit of an arbuscular mycorrhizal fungus and its host is able toachieve and maintain far higher inflow of nutrients than non-mycorrhizal roots. The colonization strategy of the mycobiont within the plant is intrinsic to the symbiosis with respect to both structural adaptations and nutrient exchange. An investigation into the effect of Glomus etunicatum colonization on the structure and phloem transport in Eragrostis curvula (Umgeni) allowed for greater insight into the dynamic of the symbiosis. The combined use of stains (such as Trypan Blue, Chlorazol Black, Safranin and Fast Green), and techniques, (such as freeze-microtome transverse sectioning and permanent slide preparations) contributed to a successful general observation of an intermediate colonization strategy using light microscopy methods. However, clarity into structural detail of mycorrhizal forms required electron microscopy studies. The SEM method used with freeze fracture was a relatively quick and simple method allowing for the observation of surface and internal features. The TEM method allowed for highresolution images providing insight into the variations in the apoplasmic compartmental form, and how this may relate to the function of the symbiosis with regard to fungal coils or arbuscules. The apoplasmic nature of mycorrhizas was substantiated and no symplasmic connections were found between symbionts. Fluorescence studies demonstrated that 5,6-carboxyfluorescein was transported through the phloem into the roots of E. curvula, but remained predominantly in the root phloem. Unloading only occurred in optimal nutrient exchange areas of meristimatic lateral or apical growth regions. It was not possible, using fluorescence techniques and related equipment available, to conclusively establish if there were symplasmic connections between the mycobiont and its host or if bidirectional transfer of nutrients occurred at the same interface.
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- Date Issued: 2007
The effect of geography, cultivation and harvest technique on the umckalin concentration and growth of pelargonium sidoides (Geraniaceae)
- Authors: White, Andrew Graeme
- Date: 2007
- Subjects: Pelargoniums , Geraniaceae , Botany -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Eastern Cape , Medicinal plants -- South Africa -- Eastern Cape , Coumarins
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4234 , http://hdl.handle.net/10962/d1003803 , Pelargoniums , Geraniaceae , Botany -- South Africa -- Eastern Cape , Traditional medicine -- South Africa -- Eastern Cape , Medicinal plants -- South Africa -- Eastern Cape , Coumarins
- Description: Pelargonium sidoides DC. (Geraniaceae) root extracts are used in the Eastern Cape Province of South Africa as a traditional medicine for the treatment of respiratory tract and gastro-intestinal infections. Ethanolic extracts are used globally as herbal treatments for bronchitis, asthma and as an immune system booster. Despite documented exploitation of wild populations by illegal harvesters, this species has not been awarded a protected status. The high level of harvest in the years preceding this study prompted this investigation of the prospects for sustainable root harvest through wild harvest and greenhouse cultivation. A novel method was developed for the purification of umckalin, a bioactive constituent in root extracts, such that the root umckalin concentrations of wild and cultivated plants could be quantified by HPLC. As part of the cultivation experiments, the concentration of umckalin in roots was measured for plants across part of the species’ distribution range in the Eastern Cape Province. This survey revealed that root umckalin concentrations were inversely related to the average annual rainfall of the collection site (r² = 0.94, p = 0.007) and directly related to soil pH (r² = 0.97, p = 0.002). Thus, the possibility of inducing high umckalin concentrations in greenhouse-cultivated plants was investigated by subjecting plants to rapid and prolonged water stress treatments. Two leaf applied hormone treatments (cytokinin and gibberellin) and a root competition treatment with a fast growing annual (Conyza albida) were also investigated based on the potential function of umckalin in P. sidoides plants. These five treatments did not significantly affect root umckalin concentrations compared to well-watered controls. The results of further experiments suggested that umckalin production may have been influenced by the geographical origin and genetics of plants rather than environmental variation. Following wild harvest experiments, the regrowth of replanted shoots from which a standard proportion of the root was harvested showed that water availability affected shoot survival but not root regrowth rate. Regrowth rates were low, questioning the viability of wild harvest. In contrast, greenhouse cultivated plants showed ca. six times greater growth rates, supporting the cultivation of roots to supply future market demand.
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- Date Issued: 2007
Drought responses of C3 and C4 (NADP-ME) Panicoid grasses
- Authors: Frole, Kristen Marie
- Date: 2008
- Subjects: Botany -- Research , Grasses -- Physiology -- South Africa , Grasses -- Effect of drought on , Grasses -- Drought tolerance , Plant-water relationships
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4193 , http://hdl.handle.net/10962/d1003762 , Botany -- Research , Grasses -- Physiology -- South Africa , Grasses -- Effect of drought on , Grasses -- Drought tolerance , Plant-water relationships
- Description: The success of C₄ plants lies in their ability to concentrate CO₂ at the site of Rubisco thereby conferring greater efficiencies of light, water and nitrogen. Such characteristics should advantage C₄ plants in arid, hot environments. However, not all C₄ subtypes are drought tolerant. The relative abundance of NADP-ME species declines with increasing aridity. Furthermore, selected species have been demonstrated as being susceptible to severe drought showing metabolic limitations of photosynthesis. However there is a lack of phylogenetic control with many of these studies. The aims of this study were to determine whether the NADP-ME subtype was inherently susceptible to drought by comparing six closely related C₃ and C₄ (NADP-ME) Panicoid grasses. Gas exchange measurements were made during a natural rainless period and a controlled drought / rewatering event. Prior to water stress, the C₄ species had higher assimilation rates (A), and water use efficiencies (WUE[subscript leaf]) than the C₃ species, while transpiration rates (E) and stomatal conductances (g[subscript s]) were similar. At low soil water content, the C₃ species reduced gs by a greater extent than the C₄ species, which maintained higher E during the driest periods. The C₄ species showed proportionally greater reductions in A than the C₃ species and hence lost their WUE[subscript leaf] and photosynthetic advantage. CO₂ response curves showed that metabolic limitation was responsible for a greater decrease in A in the C₄ type than the C₃ type during progressive drought. Upon re-watering, photosynthetic recovery was quicker in the C species than the C₄ species. Results from whole plant measurements showed that the C₄ type had a significant whole plant water use efficiency advantage over the C₃ type under well-watered conditions that was lost during severe drought due to a greater loss of leaf area through leaf mortality rather than reductions in plant level transpiration rates. The C₃ type had xylem characteristics that enhanced water-conducting efficiency, but made them vulnerable to drought. This is in contrast to the safer xylem qualities of the C₄ type, which permitted the endurance of more negative leaf water potentials than the C₃ type during low soil water content. Thus, the vulnerability of photosynthesis to severe drought in NADP-ME species potentially explains why NADP-ME species abundance around the world decreases with decreasing rainfall.
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- Date Issued: 2008
Life history, population dynamics and conservation status of Oldenburgia grandis (Asteraceae), an endemic of the Eastern Cape of South Africa
- Authors: Swart, Carin
- Date: 2008
- Subjects: Compositae , Fynbos ecology -- South Africa -- Eastern Cape , Endemic plants -- South Africa -- Eastern Cape , Rare plants -- South Africa -- Eastern Cape , Plant populations -- South Africa -- Eastern Cape , Vegetation dynamics -- South Africa -- Eastern Cape , Plant conservation -- South Africa -- Eastern Cape , Endangered species -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4230 , http://hdl.handle.net/10962/d1003799 , Compositae , Fynbos ecology -- South Africa -- Eastern Cape , Endemic plants -- South Africa -- Eastern Cape , Rare plants -- South Africa -- Eastern Cape , Plant populations -- South Africa -- Eastern Cape , Vegetation dynamics -- South Africa -- Eastern Cape , Plant conservation -- South Africa -- Eastern Cape , Endangered species -- South Africa -- Eastern Cape
- Description: Oldenburgia grandis is a rare, long-lived woody paleoendemic of the Fynbos Biome of South Africa. Confined to quartzite outcrops, it has a small geographic range and narrow habitat specificity. O. grandis responds to its fire-prone environment by resprouting. Elasticity analysis of O. grandis reveals that growth and fecundity were traded off for persistence of adult, mature and sapling stages. Morphological adaptations such as a corky fire-resistant bark and the ability to resprout after fire are traits that O. grandis have evolved to persist in a frequently disturbed environment. Population growth rate for sites undisturbed by fire for a number of years (l = 1.01) and sites at various stages of recovery after fire (l = 1.00) were very similar. The highest variation in transition probabilities for all sites was seen in the persistence of the seedling stage and growth from seedling to sapling. Observed population structure and stable stage distribution determined by the matrix model show that sites recently undisturbed by fire had high abundances of the adult and sapling stages. A peak in sapling stages was seen for the stable stage distribution where similar peak in sapling numbers were seen for population structures of sites at various stages of recoveryafter fire. Favourable environmental conditions for the persistence of O. grandis populations include no fire with transition probabilities between the observed minimum and maximum and fire frequency at a 10 year interval where seedling protection from the fire is high and adult and mature mortalities during the fire are low. Stochastic environmental events that could put populations (particularly small populations) at an increased risk of extinction include high to moderate fire intensities where seedling protection from the fire is low and adult and mature mortalities are high as a result of the fire.
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- Date Issued: 2008
Photosynthetic and growth response of C₃ and C₄ subspecies of Alloteropsis semialata to nitrogen-supply
- Authors: Abraham, Trevor Ian
- Date: 2008
- Subjects: Photosynthesis , Plants -- Effect of nitrogen on , Growth (Plants) , Plant ecology
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4182 , http://hdl.handle.net/10962/d1003750 , Photosynthesis , Plants -- Effect of nitrogen on , Growth (Plants) , Plant ecology
- Description: The greater photosynthetic nitrogen use efficiency (PNUE) of C4 compared with C3 plants may explain the relative success of C4 grasses in nutrient poor environments. This study compared the responses in photosynthetic parameters, leaf nitrogen and biomass allocation between the C3 and C4 subspecies of Alloteropsis semialata supplied soil nitrogen at three levels. Photosynthesis was assessed by means of CO2 response curves and the leaf nitrogen content assayed. Plants were destructively harvested, leaf areas determined and the dry biomass of functional plant components was measured. Results confirmed that the higher PNUE of C4 plants allowed them to accumulate more biomass than C3 plants at the high nitrogen level, despite smaller leaf areas. The greater productivity of C4 plants enabled them to invest more in storage and sexual reproduction than in leaves when compared to the C3 plants. In contrast the C3 plants invested biomass in less efficient and more nitrogen demanding leaves and bigger root systems. PNUE and photosynthetic rates were not significantly affected by nitrogen-limitation in either subspecies and the major response was a decrease in biomass accumulation and an increase in biomass allocation to roots. This altered root to shoot ratio was accompanied by a lowered allocation to sexual reproduction in the C4 subspecies, but an unaltered allocation to leaves, while in the C3 subspecies there was a decrease in leaf allocation. In a further experiment, the C4 subspecies was supplied three levels of nitrogen provided as nitrate, or alternatively as ammonium plus nitrate, and leaves were excised to within 5 cm of the ground at the start of treatment. Prior to flowering, photosynthesis was assessed by means of CO2 response curves and the plants were destructively harvested. Leaf areas and the dry biomass of functional plant components were determined, and at levels of nitrogen supply higher than those found in savanna soils the rate of photosynthesis was increased. Leaf re-growth was reduced by severe nitrogen limitation and co-provision of nitrate and ammonium had no significant effect other than increased tillering. Both subspecies of Alloteropsis semialata are adapted to nutrient poor environments and maintain photosynthetic rates by reducing leaf area. The C4 subspecies is likely to show greater resilience in disturbance-prone environments by exploiting its higher PNUE to allocate greater resources to storage and sexual reproduction, while the C3 subspecies is usually found in environments with closed canopies which favour vegetative growth, and allocate greater resources to leaves and roots.
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- Date Issued: 2008
Plant aphid interactions : effects of diuraphis noxia and rhopalosiphum padi on the structure and function of the transport systems of leaves of wheat and barley
- Authors: Saheed, Sefiu Adekilekun
- Date: 2008
- Subjects: Russian wheat aphid Rhopalosiphum padi Aphids -- Host plants Wheat -- Diseases and pests
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4225 , http://hdl.handle.net/10962/d1003794
- Description: The infestation of the cultivated grain crops by phloem feeding aphids has generated a great deal of interest over the years, due to the serious damage they cause to the crops and yield losses that result. The mechanism of the interaction between aphids and host plants remains largely unknown in spite of efforts to understand the basis of aphid feeding on grain crops. Greater efforts are required to explain the mechanism(s) of this interaction in order to achieve sustainable agriculture. This thesis focused on an investigation of the mechanism of feeding by the Russian wheat aphid, Diuraphis noxia Mordvilko (RWA) and the bird cherry-oat aphid, Rhopalosiphum padi L. (BCA) on barley and wheat cultivars. These two aphids co-occur naturally, but they inflict very different feeding effects on host plants. Structural and functional approaches were employed to investigate their feeding habits and these were then related to the observed differences in their host plants. Transmission electron microscopy (TEM) techniques were used to study the ultrastructural damage, while fluorescence microscopy techniques – using aniline blue fluorochrome (a specific stain for callose) and 5, 6-CFDA (a phloem-mobile fluorophore) – were employed to investigate the functional response to damage via wound callose formation and phloem transport capacity respectively. RT-PCR and quantitative real-time RT-PCR techniques were used to investigate the regulation of the genes involved in callose synthesis and degradation at the transcriptional level. Morphological observation of the damage caused by the aphids show that infestation by RWA results in extensive leaf chlorosis, necrosis and rolling, while infestation by BCA does not lead to any observable symptoms within the same period. Interestingly, the population study shows that BCA breeds faster than RWA within the two-week experimental period. The ultrastructural study of feeding damage caused by the two aphids on the vascular bundles of susceptible barley cv Clipper, shows a different patterns of damage. Probing the vascular bundles results in the puncturing of vascular parenchyma by both aphids, but severe damage occurs in sieve tubes-companion cell complex during sustained feeding by RWA. In contrast, less damage occurs when BCA feeds on the phloem. Drinking from the xylem by RWA results in deposition of a large quantity of electron-dense watery saliva, which apparently seals the xylem vessels completely, by blocking all the pit membrane fields between the xylem vessels and associated parenchyma cells. In contrast, drinking from xylem by BCA results in deposition of a dense, granular saliva into the xylem vessels only, which does not appear to totally occlude the pit membrane fields. This is the first known report in which ultrastructural evidence of aphids’ drinking in xylem is provided. The comparative effects of RWA feeding on a susceptible Betta and resistant Betta-Dn1 wheat cultivars showed that after two weeks, the Betta cultivar expressed damage symptoms such as chlorosis, necrosis and leaf roll, while few chlorotic patches and necrotic spots occur in resistant Betta-Dn1 cultivars. An ultrastructural investigation of the feeding damage caused to all leaf tissues revealed, for the first time, that RWA is capable of both intra- and inter-cellular probing within mesophyll cells. Probing in the mesophyll cells induces a more severe damage in susceptible Betta than in the resistant Betta-Dn1 counterpart. Similar differences in damage occurred during feeding in the thin-walled sieve tubes of the phloem, with the sieve tubes of the Betta showing more damage than that of the resistant Betta-Dn1. However, drinking from xylem resulted in the characteristic occlusion of metaxylem vessels by copious deposition of saliva by RWA in both Betta and Betta-Dn1 cultivars. In all cases of probing, feeding, and drinking by RWA in both cultivars, all probed cells with evidence of salivary material deposit and those cells adjacent to salivary material deposit, exhibit significant damage in susceptible Betta cultivar, whereas similar cells in Betta-Dn1 cultivars do not show as damage as severe. Investigation of the functional response of the plants to feeding by aphids through the deposition of wound-induced callose shows that formation and deposition of wound callose occurs in both longitudinal and cross veins within 24h of feeding by RWA. This deposition increases through short-term feeding (72h) and prolonged feeding (14d). This is in sharp contrast to the observations with BCA feeding,where little or no callose formation occurs within the same time frame. Callose formation and deposition occurs only when a higher population of BCA feeds on barley leaves. This is the first report of aphid-induced wound callose by BCA. In all cases of callose deposition, aphid stylet tracks were associated with callose and the deposition of callose appears to be a permanent feature, because wound callose remained in the leaf tissues even after 120h of the aphids’ removal. Wound callose signals (defence and anti-defence) are discovered to be transported in the phloem tissues and are dependent on the direction of assimilate flow. Examination of the possible regulation of wound callose genes at the transcriptional level shows that the two expressed glucan synthase gene sequences (GSL – genes involved in callose formation) analysed did not show any significant increase or regulation upon aphid infestation. Contrary to expectation, all three aphid-induced β-1, 3-glucanases (genes which are thought to be involved in callose degradation) showed higher expression in RWA-infested tissue than in BCA-infested tissue. The results of the feeding damage on the transport capacity of the phloem shows that BCA infestation does not lead to a significant reduction in the phloem transport capacity during short-term feeding (72h), while RWA-infested leaves showed considerable reduction in the transport capacity of the phloem within the same period. However, prolonged feeding (14d) by BCA induces a considerable reduction on the transport capacity of the phloem on the infested tissues. In contrast, a marked reduction in the transport capacity of the phloem occurs in RWA-infested leaves and in most cases, complete cessation of transport ensues. In conclusion, these data collectively suggest that RWA is a serious and most destructive phloem feeder in comparison to the BCA. RWA causes severe damage to all cellular tissues of the host plants, which result in apoplasmic and symplasmic isolation of xylem and phloem tissues, while BCA infestation does not result in such isolation within the same time and population levels. Resistance genes appear to function by conferring resistance to cell damage on the resistant cultivars during aphid feeding. Responses by plants to aphid infestation via wound callose deposition are again shown to be species-specific. A quick response results when RWA feeds, even at a very low population level, while a response occurs only at a higher infestation level by BCA, and this response was shown as not regulated at the transcriptional level. Differences in the damage to leaf tissues and wound callose deposition eventually lead to varying degrees of damage to the transport capacity of the phloem. These differences in the damage signatures are hereby suggested to be the cause of the diversity in the observed damage symptoms and the yield losses upon infestation by the two aphid species.
- Full Text:
- Date Issued: 2008
The zonation of coastal dune plants in relation to sand burial, resource availability and physiological adaptation
- Authors: Gilbert, Matthew Edmund
- Date: 2008
- Subjects: Sand dune conservation -- South Africa -- Eastern Cape Coastal ecology -- South Africa -- Eastern Cape Botany -- South Africa -- Eastern Cape Coastal biology -- South Africa -- Eastern Cape Littoral plants -- South Africa -- Eastern Cape Littoral plants Sand dune plants -- Ecophysiology Sand dune plants -- Geographical distribution
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4195 , http://hdl.handle.net/10962/d1003764
- Description: When considering the large amount of work done on dune ecology, and that a number of the classical ecological theories originate from work on dunes, it is apparent that there remains a need for physiological and mechanistic explanations of dune plant phenomena. This thesis demonstrated that in the extreme coastal environment dune plants must survive both high rates of burial (disturbance), and low nutrient availability (stress). The ability of four species to respond to these two factors corresponded with their position in a vegetation gradient on the dunes. A low stem tissue density was shown to enhance the potential stem elongation rate of buried plants, but reduced the maximum height to which a plant could grow. Such a tradeoff implies that tall light-competitive plants are able to survive only in stable areas, while burial responsive mobile-dune plants are limited to areas of low vegetation height. This stem tissue density tradeoff was suggested as the mechanism determining the zonation that species show within the dune vegetation gradient present at various sites in South Africa. Finally, detailed investigations of dune plant ecophysiology found that: 1) The resources used in the response to burial derive from external sources of carbon and nitrogen, as well as simple physiological and physical mechanisms of resource allocation. 2) The leaves of dune plants were found to be operating at one extreme of the photosynthetic continuum; viz efficient use of leaf nitrogen at the expense of water loss. 3) Contrary to other ecosystems, the environmental characteristics of dunes may allow plants to occupy a high disturbance, high stress niche, through the maintenance of lowered competition. 4) At least two mobile-dune species form steep dunes, and are able to optimise growth, on steeper dunes, such that they have to grow less in response to burial than plants that form more shallow dunes. In this thesis, it was shown that the link between the carbon and nitrogen economies of dune plants was pivotal in determining species distributions and survival under extreme environmental conditions. As vast areas of the world’s surface are covered by sand dunes these observations are not just of passing interest.
- Full Text:
- Date Issued: 2008
Photosynthetic and evolutionary determinants of the response of selected C3 and C4 (NADP-ME) grasses to fire
- Authors: Martin, Tarryn
- Date: 2009
- Subjects: Photosynthesis , Carbon -- Metabolism , Grasses -- Adaptation , Plants -- Effect of fires on , Grasses -- Research , Grasses -- Physiology , Grasses -- Evolution , Grasslands -- Research
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4211 , http://hdl.handle.net/10962/d1003780 , Photosynthesis , Carbon -- Metabolism , Grasses -- Adaptation , Plants -- Effect of fires on , Grasses -- Research , Grasses -- Physiology , Grasses -- Evolution , Grasslands -- Research
- Description: Species possess characteristics that are considered adapted to burning and these allow them to outcompete species and dominate in fire prone environments. It has therefore been proposed that fire might have played a critical role in the observed expansion of the grasslands, during the late Miocene. The aim of this study was (i) to investigate whether plant response to fire was a result of physiology or (ii) whether it was due to phylogenetic history. This was achieved by doing a pair-wise comparison between Panicoideae (and Panicoideae) and non-Panicoideae (Danthonioideae and Aristidoideae) species. Pre-fire characteristics, that would enhance fire frequency and assist with plant recovery after burning, were compared across phylogenies and photosynthetic type. Post fire plant recovery was then followed in a field and pot comparison which examined the re-growth of the leaf canopy area, leaf mass, above-ground biomass and the cost of this to the below-ground biomass. The pre-fire characteristics showed both a photosynthetic and phylogenetic response. It was found that the species showed a greater canopy death during winter and had a lower moisture content than the species. These characteristics would potentially contribute towards a larger fuel load in the species. However, the comparison of the dead standing biomass at the end of winter and the below-ground biomass, showed a phylogenetic response with the Panicoideae having a proportionally larger dead standing biomass and below-ground biomass than the non-Panicoideae. These results suggest that not only did the Panicoideae have a larger potential fuel load but that they also shunted carbon below-ground, enabling a fast recovery after being burned. The post-fire results were more strongly determined by phylogeny than by photosynthetic type. The Panicoideae recovered faster and more completely than the non-Panicoideae grasses, possibly contributing to their success and expansion under conditions of increased fire frequency. Although recovery of the and Panicoideae were similar, frequently burnt grasslands are dominated by the Panicoideae. Hence, this dominance cannot be explained by differences in their fire responses and may be determined by the post-fire environmental conditions that potentially advantage species possessing the photosynthetic pathway. Panicoideae dominance is limited to mesic environments where fire is the likely driver of grassland expansion while more arid environments are dominated by non-Panicoideae species. Representative species from these non-Panicoid subfamilies showed poor recovery after fire. This suggests that factors other than fire were the likely drivers of these xeric grassland expansions. The ability of these subfamilies, and particularly the species, to cope with drought remains a likely selective mechanism that requires further research.
- Full Text:
- Date Issued: 2009
Contrasting biodiversity values in four states of Eastern Province thornveld
- Authors: Duncan, Imogen May
- Date: 2010
- Subjects: Biodiversity -- South Africa -- Eastern Cape , Agrobiodiversity -- South Africa -- Eastern Cape , Agricultural ecology -- South Africa -- Eastern Cape , Veld -- South Africa -- Eastern Cape , Landscape assessment -- South Africa -- Eastern Cape
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4190 , http://hdl.handle.net/10962/d1003759 , Biodiversity -- South Africa -- Eastern Cape , Agrobiodiversity -- South Africa -- Eastern Cape , Agricultural ecology -- South Africa -- Eastern Cape , Veld -- South Africa -- Eastern Cape , Landscape assessment -- South Africa -- Eastern Cape
- Description: Land use and land transformation are major threats to biodiversity. Only a small percentage of land and thus biodiversity is protected within reserves. The majority of biodiversity lies in the hands of private and communal farmers and in order to protect biodiversity they must perceive it as having some value and have the means and incentive to conserve it. This study examined two things: (i) the relationship between biodiversity and measures of ecosystem health, range condition, primary production and presence of useful plants that would be expected to be of relevant use to land users, (ii) the perceptions of farmers of vegetation states that differ in the abovementioned attributes. Within the Eastern Province Thornveld of the Smaldeel area, four different vegetation states were selected for the study, namely park-like grassland with scattered Acacia karroo (“savanna”), heavily infested Acacia karroo grassland (“acacia”), thicket-grassland mosaic (“thicket”) and heavily utilised thicketgrassland in communal lands (“communal”). The four states are a consequence of different patterns of browsing and fire, in both pre-colonial and recent times. Different ecological attributes were assessed and compared for each state and the relationships between the different attributes determined. Ecosystem health, in terms of stability or resistance to erosion, infiltration/water-holding capacity, and nutrient cycling were compared using Landscape Function Analysis. The agricultural value of the different landscapes was measured using range condition assessment techniques. Plant species richness and other measures of diversity, along with their conservation and usefulness values, were compared between states. Plant productivity and biomass were compared using satellite data. The thicket state was found to be the most functional due to the added habitat complexity provided by the vegetation. It was the most biodiverse, the most useful and contained many, but not all of the important conservation species. The communal state had high biodiversity and was be fairly resilient to heavy usage, not showing the expected signs of land degradation. The savanna state, although thought of as the optimum state for cattle production, was not significantly different from the other states in terms of agricultural potential, but had the lowest values for plant diversity, browse potential, abundance of useful plant species and biomass. The acacia state had the highest and least stable values in terms of biomass production, however it was found to contain species of conservation importance. The preference that four groups of land users, namely men and women from commercial and communal farming areas, expressed for the four vegetation states was assessed using semi-structured interviews in conjunction with A3 colour photographs. The men and women from the communal areas and the men from the commercial areas valued the thicket state highly for its farming potential. The male commercial farmers also valued the savanna state highly as they perceived it as being most productive for cattle farming. Both the thicket state and the savanna state were found aesthetically pleasing by all the user groups, in line with theories of preference for modified savannas and for familiar environments. There appears to be potential for preserving biodiversity on farmland. The farmers in this study, with their very utilitarian perspective, were found to intuitively gauge the health of the landscape and recognise biodiversity as indicating good farming land. The commercial farmers were strongly influenced by economic motives and thus attracted to the savanna state, but also recognised the opportunity for a wider variety of farming activities in the thicket state. The communal farmers have a high dependence on the land for their livelihoods and preferred the thicket state for its overall usefulness. The views of the farmers indicate that the opportunity for conservation is good, however much of the thicket state lies in the communal land, where the openaccess land use system makes managing for biodiversity difficult.
- Full Text:
- Date Issued: 2010
Cost-effective, post-mining environmental restoration of an open-cast phosphate mine at Langebaanweg, South Africa
- Authors: Van Eeden, Joseph Deon
- Date: 2010
- Subjects: Abandoned mined lands reclamation -- South Africa -- Langebaan , Phosphate mines and mining -- Environmental aspects -- South Africa -- Langebaan , Phytoremediation -- South Africa -- Langebaan
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4232 , http://hdl.handle.net/10962/d1003801 , Abandoned mined lands reclamation -- South Africa -- Langebaan , Phosphate mines and mining -- Environmental aspects -- South Africa -- Langebaan , Phytoremediation -- South Africa -- Langebaan
- Description: Approaching the ecological rehabilitation of an open-cast phosphate mine in the West Coast of South Africa during the post-operational phase presented some challenges. The area was extensively modified during the mining operations. Soils from different layers were mixed with topsoil being covered by subsoil, overburden dumps and tailing dams being constructed resulting in extensive cross-zoned soils. Large areas of subsoil areas were exposed on the mine floor with localized and small scale salinity being evident. The modified topography as well as the complex new surface material posed a challenge in terms of identifying suitable local species that could be used to rehabilitate the post-mining environment. The mine area was heavily infested with woody alien invasive plants, such as Acacia cyclops, established in an attempt to reduce the dust and little natural vegetation cover was present. In the arid west coast environment, the four-month-long winter growing season is followed by hot and windy dry summers (Chapter 2) presenting a challenge reestablishing local vegetation in modified soils. Moreover, little was known about the local vegetation in terms of their propagation and use in stabilization techniques as an alternative to exotic vegetation such as the A. cyclops, which had been more often used in revegetation projects. A study was conducted to determine the most efficient and cost-effective methods of vegetative rehabilitation of the Chemfos site (Chapter 1). A review of the literature available at the time as well as approaches that were successfully implemented in other Western Cape rehabilitation projects such as the Du Toitskloof Pass and the Sishen–Saldanha railway line (Chapter 3), were considered. Previous studies on the west coast dunes at Blaauwberg had shown using Marram grass as a dune stabilizer was most successful. Marram grass was tested in trials alongside local grasses, such as Chaetobromus dregeanus and Ehrharta villosa, that showed potential but had not been formally evaluated. The environmental context of Chemfos (Chapter 2) as well as the Conceptual Rehabilitation Plan that considered the modified environment, soils and closure objectives of the mine, were reviewed to determine the most pressing rehabilitationrelated questions that required answers. This led to the final experimental design that was implemented mid-winter in 1996 (Chapter 5). The trials were implemented in the areas perceived to be the most difficult to rehabilitate, namely the mobile sands in the tailings dam and the exposed subsoil or mine floor areas. The use of brushwood together with specific plants and seeds appropriate for the use in either sandy soil or subsoil were evaluated in a variety of combinations and application densities to determine the most effective treatment combination at the minimum effective density. The best initial cover of the tailings dam were recorded in the Ammophila arenaria trials but the use of the local grass species Ehrharta villosa, performed better from year two onwards and was much cheaper to establish. On the subsoil, the trials where a cover of topsoil was used performed better than the combination trials. This indicated that topsoil placement on post-operational phase shaped subsoils during the mining operation to be the most desirable treatment. Initial results of the trials were used as a basis for developing the rehabilitation techniques that were rolled out across the Chemfos landscape. The approaches were refined as indications of trial responses became evident. Lessons learned were incorporated in the adaptive management approach that was followed and the rehabilitation techniques (Chapter 6) were continually re-evaluated and adjusted. This resulted in a significant step towards achieving the overall research objective of finding cost-effective approaches to rehabilitation. Components such as refinement of the seed collection and processing techniques (Chapter 7) where the post-harvest processing cost was significantly reduced by introducing specially designed drying racks. Processing techniques were adjusted to suit the different species, and a variety of mechanical processing options were explored. The scale of the Chemfos project led to the development of new techniques of manufacturing a smoke-derived germination stimulant (Chapter 8) since commercial availability of these products was very limited. The development of FireGrow assisted in the overall aim of reducing cost by increasing germination of seed in the rehabilitation sites using a very cost-effective smoke concentrate. Socio-economical aspects were considered during the implementation as well as the post-closure phases of the rehabilitation and BHPBilliton invested through the agency of the SAMANCOR Trust. This led to the development of livelihoods of the staff that remained in the area and that lived in the mine village. The demography of the population has changed over time in the Green Village as well as the skills that the inhabitants have developed. Thus, the new economic opportunities that were pursued have brought a new lease on life beyond the lifespan of the mine (Chapter 9) once the closure certificate had been issued.
- Full Text:
- Date Issued: 2010
Ecology and degree of specialization of South African milkweeds with diverse pollination systems
- Authors: Coombs, Gareth
- Date: 2010
- Subjects: Milkweeds -- South Africa Milkweeds -- South Africa -- Ecology Milkweeds -- South Africa -- Pollination Allee effect Self-pollination Pollination by insects
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4189 , http://hdl.handle.net/10962/d1003758
- Description: Like orchids, the complexity of flowers found in asclepiads (Asclepiadoideae, Apocynaceae) and the fact that pollen is presented as pollinaria, offers excellent opportunities to study various aspects of plant-pollinator interactions. In this thesis I investigated two broad themes: ecological aspects of the pollination biology of hymenopteran and fly-pollinated asclepiads as well as the degree of specialization to certain pollinators in these species. Colonizing plants often reproduce through self-pollination, or have highly generalized pollination systems, or both. These characteristics facilitate establishment in small founding populations and generates the prediction that reproductive success should be independent of population size in these species. Chapter one examines the pollination biology of Gomphocarpus physocarpus, an indigenous, weedy species and investigates the relationship between reproductive success and population size. In this species, there is no evidence of an Allee effect and reproductive success is not correlated with population size. In addition G. physocarpus is not capable of self-pollination, suggesting it is completely reliant on pollinators for seed set. The lack of a relationship between pollination success and population size is therefore likely explained by the generalized wasp pollination system of this species. Several milkweeds are invasive outside of their native ranges. Invasive species either need to co-opt native pollinators in order to reproduce or reduce their reliance on pollinators through having the ability to self-pollinate. Co-opting native pollinators is expected to be easier in species that have generalized pollination systems, alternatively species with specialized flower morphologies need to rely on similar functional groups of pollinators to be present within the invaded range. Chapter two investigates the pollination biology and pollination success of the invasive milkweed, Araujia sericifera, and finds that in South Africa, this species is visited mainly by native honeybees and nocturnal moths. Moths however contribute little to pollen removal, and deposition. Based on the apparent morphological mismatch between the flower of A. sericifera and native honeybees, I propose that the native pollinators of this species are likely to be larger Hymenoptera (e.g. Bumblebees). Data from a breeding system study, indicated that this species is not capable of automatic self-pollination, but could set fruit from geitonogamous self-pollinations pointing to the importance of native pollinators for successful reproduction. The pollinaria of milkweeds can accumulate on pollinators to form pollen masses large enough to physically interfere with the foraging behaviour of pollinating insects. In chapter three I describe the pollination biology of Cynanchum ellipticum and find that this species is mainly pollinated by honeybees although this species is visited by several other members of Hymenoptera, Lepidoptera and Diptera. Due to the structure of the pollinaria, these chain together relatively efficiently and frequently form large pollinarium loads on the mouthparts of honeybees. However there is little evidence that these pollinarium loads influence the foraging times of pollinators and only a few individual honeybees exhibited longer foraging times and most honeybees were unaffected by the presence of large pollinarium loads. Within the genus Cynanchum there is large variation in the gynostegium structure that may influence the pattern of pollinarium loading on pollinators as well as pollen reception as shown in chapter three. In Chapter four, the pollination biology of Cynanchum obtusifolium is examined, and like that of C. ellipticum, this species is visited by a wide diversity of pollinators but honeybees appear to be the primary pollinators. More importantly this species is shown to be andromonoecious and produces two morphologically different flower types, that may be distinguished based on differences in the gynostegium structure. These two types of flower could mainly be distinguished by the length of the anther wings. I found that flowers with short anther wings function as male flowers by only exporting- and rarely receiving pollinia. Flowers with longer anther wings function as hermaphrodite flowers and can both export and receive pollinia. The ratio of male to hermaphrodite flowers varied at different times during the flowering season, but preliminary data suggested that this was not related to levels of pollination success. The genera Stapelia and Ceropegia are well known for their intricate floral adaptations that mimic the brood and feeding substrates of pollinating flies. Despite several studies that have documented the various adaptations to fly pollination in different species, there is a lack of natural history studies documenting different flower visitors, pollen loads and long term levels of pollination success in these species. In Chapter six I document the pollination biology of Ceropegia ampliata by documenting different pollinators and quantifying average levels of pollination success and the nectar reward. I also experimentally manipulated the trapping hairs of this species to determine whether trapping hairs influence average levels of pollen export and receipt. I show that Ceropegia ampliata is pollinated by a generalist guild of flies (mainly Tachinidae, Sarcophagidae, Muscidae and Lauxaniidae) and produces minute quantities of relatively dilute nectar as a reward. Pollination success was generally low in this species and increases periodically suggesting that the abundance of pollinators is patchy. I found that flowers with trapping hairs that had already wilted had higher levels of pollinarium removal than flowers with erect hairs, however experimentally removing the hairs had no significant effect on pollen export and receipt. In Chapter seven, I document the pollinators, pollen loads and long term levels of pollination success in Stapelia hirsuta var. bayllissi, a rare sapromyiophilous stapeliad. I find that, in contrast to C. ampliata, this species was specialized to pollination by small flies of the family Anthomyiidae. Similar to the results from Chapter seven, I find that long term levels of pollination success were typically low but could increase periodically, although such increases were generally unpredictable. There are currently very few records documenting pollinator interactions in the Periplocoideae. Many species within this subfamily exhibit open-access flowers suggestive of pollination by short-tongued insects. I investigated the pollination biology of Chlorocyathus lobulata, a rare species with a highly localized distribution. I aimed to determine the pollinators, average levels of pollination success and demography of this species in order to determine whether this rare species is suffering from the collapse of a highly specialized pollinator mutualism. I also quantified the high incidence of flower herbivory caused by larvae of the moth, Bocchoris onychinalis. I find that C. lobulata has a highly generalized fly pollination system and average levels of pollination success suggested that a large proportion of flowers had pollen removed and deposited suggesting that this species is not experiencing pollination failure. The large numbers of juveniles present also indicated that recruitment is taking place.
- Full Text:
- Date Issued: 2010
Effects of treatment on Lantana camara (L.) and the restoration potential of riparian seed banks in cleared areas of the Victoria Falls World Heritage Site, Livingstone, Zambia
- Authors: Nang'alelwa, Michael Mubitelela
- Date: 2010
- Subjects: Lantana camara -- Victoria Falls (Zambia and Zimbabwe) , Lantana camara -- Biological control -- Victoria Falls (Zambia and Zimbabwe) , Invasive plants -- Biological control -- Victoria Falls (Zambia and Zimbabwe) , Riparian restoration -- Victoria Falls (Zambia and Zimbabwe) , Riparian ecology -- Victoria Falls (Zambia and Zimbabwe)
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4217 , http://hdl.handle.net/10962/d1003786 , Lantana camara -- Victoria Falls (Zambia and Zimbabwe) , Lantana camara -- Biological control -- Victoria Falls (Zambia and Zimbabwe) , Invasive plants -- Biological control -- Victoria Falls (Zambia and Zimbabwe) , Riparian restoration -- Victoria Falls (Zambia and Zimbabwe) , Riparian ecology -- Victoria Falls (Zambia and Zimbabwe)
- Description: The exotic plant Lantana camara L. has invaded the riparian areas of the Victoria Falls World Heritage Site in Livingstone, southern Zambia, threatening native plant communities which support populations of species of special concern. I trialled the mechanical control method of manual uprooting and 3 different herbicides applied through paint brushing of an imazapyr concentrate at 250g. l¯¹, spraying on cut stumps with metsulfron methyl at 600g.l¯¹, and foliar spraying on re-emergent lantana foliage with glyphosate at a dosage of 166g. l¯¹ in July 2008 in 20 100m2 treatment plots, 5 invaded control plots and 5 uninvaded controls. Follow-up treatments for re-sprouting lantana stumps and emerging seedlings were undertaken in June 2009. I measured effectiveness of the methods using adult lantana mortality in June 2009 and lantana seedling density in the different treatment plots during the follow-up exercise. The cost of the various methods and human labour applied were compared across the four treatments at initial clear and at follow-up. All treatments recorded a high adult lantana mortality rate, though there were no significant differences in lantana adult mortality amongst the treatments. Overall, uprooting had the highest adult mortality, followed by imazapyr, metsulfron and lastly glyphosate. Germination of lantana seedlings after clearing was high for all treatments but with no significant differences occurring between the treatments. Both adult lantana mortality and seedling density were however significantly different from the control. With labour included, chemical costs were far higher relative to uprooting, though uprooting costs were the highest when it came to the follow-up because of the emerging seedlings and some resprouting stumps. The effects of mechanical and chemical treatments on vegetation composition in the cleared areas were also assessed in order to detect any non-target and medium term effects of treatments. Contrary to expectation, none of the chemicals showed any significant effects on vegetation composition in the short and medium-term and no significant differences were found in plant species richness, diversity and seedling density between invaded and uninvaded plots at baseline, in October 2008 and in September 2009. In order to determine potential for unaided vegetation recovery in the riparian areas of the study site after lantana clearing, I conducted an investigation of soil seed banks and seed rain using 60 seed bank samples measuring 1800m³ collected from 30 invaded and uninvaded plots. Using the seedling emergence method, 1, 991 seedlings belonging to 66 species representing 27 families germinated from the seed bank. Sedges (Cyperaceae family) were the most abundant taxa in the seed banks from invaded areas, followed by Ageratum conyzoides, lantana, Triumfetta annua and Achyranthes aspera which also occurred in the uninvaded soil seed banks. The seed banks from uninvaded plots were dominated by the grass Oplismenus hirtellus. Overall, species richness, diversity and seedling density from seed banks in invaded areas did not differ significantly from seed bank in uninvaded areas and there was a low similarity in species composition when above ground vegetation was compared to seed banks from invaded and uninvaded areas. It would appear if natural regeneration occured from the current seed bank in disturbed areas, future vegetation would largely comprise of short lived, early successional species in the short term as the seed bank is dominated by non-native herbaceous weedy species. From the seed traps investigating seed rain, a total of 27 species numbering 623 individual seeds were found in the thirty 1m² seedtraps distributed in invaded and uninvaded areas at the five sites, over an intermittent period of three months. Lantana had the highest monthly arrival rate in the seed traps followed by Phoenix reclinata and Ricinus communis. The number of species with invasive potential found in the seed traps located in invaded areas was more than that found in seed traps under native vegetation cover by far. Considerable forest remnants still occur around the invaded sites, and these could serve as an important source for long-term natural re-establishment of native vegetation if seed availability by animals and wind dispersal continues, while the re-invasion of lantana is prevented by ongoing follow-ups and futher clearing of lantana invaded areas. It is concluded that while uprooting and other treatments are effective in the control of lantana, its successful control in the Victoria Falls World Heritage Site will require extensive clearing to keep it from reinvading infested areas after clearing as shown by the seed rain data. The high seedling density of lantana in the seed banks and in the cleared areas shows the need for ongoing follow-up in order to deplete soil stored seed banks. There is need for longer term research to establish what the exact follow-up requirements are in order to contain lantana re-infestation and create favourable micro-sites for native species to establish. It is predicted that ongoing lantana control in the cleared plots will most likely initiate long-term community recovery.
- Full Text:
- Date Issued: 2010
The phytogeography of the Sneeuberg, Nuweveldberge and Roggeveldberge (Great Escarpment): assessing migration routes and endemism
- Authors: Clark, Vincent Ralph
- Date: 2010
- Subjects: Phytogeography -- South Africa Endemic plants -- South Africa Plants -- Migration -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4187 , http://hdl.handle.net/10962/d1003756
- Description: The Great Escarpment forms a semi-continuous mountain system 5 000 km long, stretching from Angola in the north-west, south through Namibia, and into western, southern and eastern South Africa, including Lesotho and Swaziland. It is composed of a wide variety of geological suites but is unified in representing the edge of the African plateau and the passive Gondwanan continental margin. The Great Escarpment falls into all major climatic zones on the subcontinent, is a repository of palaeo- and neo-endemics, hosts more than half of southern Africa‟s centres of plant endemism, and has a rich suite of endemic fauna. In addition, the Great Escarpment is believed to be both a refugium and corridor for biological diversity. Despite the biological richness of the Great Escarpment, research to date has been fragmented and many sections of the Great Escarpment have not been studied. The aim of this study is to contribute to research on the Great Escarpment by undertaking a detailed floristic study of the southern Great Escarpment (the Sneeuberg, Nuweveldberge and Roggeveldberge). Together these mountains comprise approximately 1 000 km (one fifth) of the Great Escarpment, and occupy a transition zone between the summer rainfall zone in the east and the winter rainfall zone in the west. They are also the sections of Great Escarpment most closely situated to the Cape Floristic Region (CFR) and would thus be involved in hypothesised migration routes for lineages that also occur further north through the Drakensberg Alpine Centre (DAC) to the East African mountain chain. Detailed fieldwork of the southern Great Escarpment was undertaken over a period of four years in all seasons. Approximately 8 000 specimens were collected. Particular emphasis was placed on areas that may represent refugia, i.e. the highest plateaux and peaks, mesic areas and cliff-lines. An overview of each mountain range, together with their endemic plant species and phytogeography, is provided. Approximately ten new species have been discovered during this study, two of which have been described to date. Numerous endemics only known from their types have also been rediscovered. The Sneeuberg is defined as a new centre of plant endemism on the Great Escarpment (endemism of 2.3%), and the role of the Boschberg and Groot-Bruintjieshoogde (part of the Sneeuberg) as a nexus for floristic migration routes is discussed. The Nuweveldberge is shown to have low endemism despite a floristic tally similar to the Sneeuberg, while the Roggeveldberge are confirmed to be the most endemic-rich section of the southern Great Escarpment. The field data collected was augmented by available data in taxonomic revisions, and floras for the Sneeuberg, Nuweveldberge and Roggeveldberge were compiled. In order to floristically compare the southern Great Escarpment with other sections of the Great Escarpment and the CFR, a database of some 12 000 taxa was created using available floristic data for the CFR, DAC and Great WinterbergAmatolas, together with the data collated for the Sneeuberg, Nuweveldberge and Roggeveldberge. These data were analysed using phenetic methods and Parsimony Analysis of Endemicity (PAE). The results indicate stronger linkages in the east, particularly between the Sneeuberg and Nuweveldberge, and between the Sneeuberg and the Great WinterbergAmatolas. The relationship of the Roggeveldberge with the rest of the southern Great Escarpment remains ambiguous. In order to refine notions of connectivity and migration routes, 19 well-sampled phylogenies were assessed for sister-taxon disjunctions to explore CFRGreat Escarpment connections. Palaeo-connectivity between the CFR and southern Great Escarpment is most strongly supported for the south-eastern (SE) connection, and less so for the north-western (NW) and Matjiesfontein connections. There is support for the current (or recent) use of these three connections from numerous species that occur on both sides of the connections. Results of these analyses indicate that the southern Great Escarpment is a palaeo-corridor, the functioning of which has been broken by the aridification of the Nuweveldberge since the Last Glacial Maximum (LGM). Floristic connectivity is strongest in the east, from the Nuweveldberge to the DAC, and is less so in the west between the Nuweveldberge and the Roggeveldberge a finding attributed to the transition from a reliable winter rainfall regime on the Roggeveldberge to an unpredictable moisture regime on the Nuweveldberge. The mountains of the southern Great Escarpment are thus a series of refugia from a previous moister, cooler climate and are a corridor between the eastern and western components of the Great Escarpment. The SE connection is the primary link between the CFR and the eastern Great Escarpment Afromontane region in southern Africa. The implications of this research are that accurate conservation assessments and Red Data listings for many of the previously poorly-known endemics can now be made, and appropriate conservation measures implemented. Climate change remains the primary threat to these endemics and montane taxa in general, while degradation of wetlands is the primary threat to the water catchment service provided by the southern Great Escarpment. Future detailed research on the Great WinterbergAmatolas and Stormberg and a comprehensive flora of the HantamRoggeveldberge will further enhance our understanding of the floristics of the southern Great Escarpment, and provide the necessary data for comprehensive GIS-based models of proposed climate change scenarios for local, regional and national conservation planning.
- Full Text:
- Date Issued: 2010
Comparative study of the feeding damage caused by the South African biotypes of the Russian wheat aphid (Diuraphis noxia Kurdjumov) on resistant and non-resistant lines of barley (Hordeum vulgare L.)
- Authors: Jimoh, Mahboob Adekilekun
- Date: 2011
- Subjects: Aphids Russian wheat aphid -- Research -- South Africa Barley -- Diseases and pests -- South Africa
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4201 , http://hdl.handle.net/10962/d1003770
- Description: Cereal crop productivity is hampered when these plants are infested by phloem feeding aphids. A great deal of research has been carried out with the direct aim of a clearer understanding of the mechanism involved in the interaction between aphids and their host plants. Research has directly or indirectly been geared towards enhanced plant productivity and achieving sustainable agriculture. Barley (Hordeum vulgare L.) is an important small grain crop in South Africa, whose crop performance is negatively affected by fluctuations in weather patterns as well as by agricultural pests. One of the insect pests infesting barley is the Russian wheat aphid, Diuraphis noxia Kurdjumov (RWA), of which the two South African biotypes, codenamed RWASA1 and RWASA2, were studied in this thesis. During dry spells, RWA infestation becomes a more serious threat to barley productivity. Resistant plants have been used to combat RWA infestation of small grains. In South Africa, 27 RWA-resistant wheat cultivars are currently used in commercial cultivation, but no resistant barley lines have, unfortunately, been developed, in spite of this grain’s significant economic importance. This informed the study in this thesis, and this interest particularly focussed on three RWA-resistant lines developed by the USDA, testing their performance against South African RWA biotypes, for possible adaptation to South Africa. The aim was thus to examine the plant-aphid interactions, aphid breeding rates, plant damage and sustainability, evidence of resistance or tolerance and finally potential performance under elevated CO2 (a very real climate change threat). Two major avenues of research were undertaken. The first aspect involved examination of structural and functional damage caused by RWASA1 and RWASA2 on the three resistant and a non-resistant line. Aphid population growth and damage symptoms (chlorosis and leaf roll) of infestation by these aphid biotypes were evaluated. This was followed by a structural and functional approach in which the effects of feeding on the transport systems (phloem and xylem) of barley were investigated. Fluorescence microscopy techniques (using aniline blue fluorochrome, a specific stain for callose and 5,6-CFDA, a phloem-mobile probe) were applied to investigate the feeding-related damage caused by the aphids, through an examination of wound callose formation and related to this, the resultant reduction in phloem transport capacity. Transmission electron microscopy (TEM) techniques provided evidence of the extent of the feeding-related cell damage. The second aspect involved a study of the effect of changing CO2 concentrations ([CO2]) on the resistant and susceptible barley cultivars to feeding by the two RWA biotypes. Leaves of plants grown at ambient and two elevated levels of [CO2] were analysed to investigate the effect of changing [CO2] on biomass, leaf nitrogen content and C:N ratio of control (uninfested) and infested plants. The population growth studies showed that the populations of the two RWA biotypes as well as bird cherry-oat aphid (BCA, Rhopalosiphum padi L.) increased substantially on the four barley lines. BCA was included here, as it had been the subject of several previous studies. RWASA2 bred faster than RWASA1 on all lines. The breeding rates of the two RWA biotypes were both suppressed and at near-equivalent levels on the three resistant lines, compared to the non-resistant PUMA. This suggests that the resistant lines possessed an antibiosis resistance mechanism against the feeding aphids. Feeding by the aphids manifested in morphological damage symptoms of chlorosis and leaf roll. The two biotypes inflicted severe chlorosis and leaf roll on the non-resistant PUMA. In the resistant plants, leaf rolling was more severe because of RWASA2 feeding compared to RWASA1 feeding. In contrast, chlorosis symptoms were more severe during RWASA1 feeding than was the case with RWASA2 feeding. Investigation of the effect of aphid feeding on the plants showed that callose was deposited within 24h and that this increased with longer feeding exposure. Wound callose distribution is more extensive in the non-resistant PUMA than in the resistant plants. RWASA2 feeding on the resistant lines caused deposition of more callose than was evident with RWASA1 feeding. During long-term feeding, it was evident that variation in the intensity and amount of wound callose was visible in the longitudinal and transverse veins of the resistant plants. Of the three STARS plants, STARS-9301B had the least callose. Interestingly, wound callose occurred in both resistant and non-resistant plants, in sharp contrast to what has been reported on resistant wheat cultivars that were developed in South Africa. The relative reduction in the wound callose deposited in the resistant line, when compared to the non-resistant lines, suggests the presence of a mechanism in the resistant lines, which may prevent excessive callose formation. Alternatively, the mechanism may stimulate callose breakdown. RWASA2 feeding on the resistant lines deposited more wound callose than RWASA1 feeding. This evidence supports the hypothesis that RWASA2 is a resistance breaking and more aggressive feeder than RWASA1 is; and further underscores the urgent need for development of RWA-resistant barley cultivars. The ultrastructural investigation of the feeding damage showed that the two biotypes caused extensive vascular damage in non-resistant plants. There was extensive and severe cell disruption and often obliteration of cell structure of the vascular parenchyma, xylem and phloem elements. In sharp contrast, among the resistant plants, feeding-related cell damage appeared to be substantially reduced compared to the non-resistant PUMA. Low frequency of damaged cells indicated that majority of the cell components of the vascular tissues were intact and presumed functional. There was evidence of salivary material lining the secondary walls of the vascular tissue, which resulted in severe damage. Within xylem vessels, saliva material impregnated half-bordered pit pairs between the vessels and adjacent xylem parenchyma. This is believed to prevent solute exchange through this interface, thereby inducing leaf stress and vi leaf roll. A notable finding is that RWASA2 effectively induced more cell damage to vascular tissues in the resistant lines than did RWASA1. In general the experimental evidence (see Chapter 5) suggests that the resistant lines are possibly more tolerant (or able to cope with) to RWA feeding. Evidence for this is the reduction of wound callose and at the TEM level, a comparatively less obvious cell damage in the resistant lines, which suggests that they possess antibiosis and tolerance capacity. The apparent reduction of feeding-related cell damage from the TEM study confirmed the disruptive action of the feeding aphids in experiments using the phloem-mobile probe, 5,6-CF. Results showed that feeding by RWASA1 and RWASA2 reducedthe transport functionality of the phloem in all cases, but that RWASA2 feeding caused a more obvious reduction in the rate and distance that 5,6-carboxyfluorescein was transported, than did RWASA1. Investigation of the effect of changing [CO2] on the barley cultivars showed that in the absence of aphids and under elevated CO2 conditions, the plants grew more vigorously. In this series of experiments, the infested plants suffered significant reduction in biomass under ambient (as was expected) and under the two elevated CO2 regimes. Biomass loss was greater at elevated CO2 than under ambient [CO2]. The infested nonresistant PUMA plants showed a more significant biomass loss than did the resistant cultivars. Clearly, the benefits derived from elevated CO2 enrichment was thus redirected to the now-advantaged aphids. Uninfested vii plants showed an increase in leaf nitrogen under the experimental conditions. However, feeding aphids depleted leaf nitrogen content and this was more apparent on plants exposed to RWASA2 than was the case with RWASA1. The end result of this was that C:N ratio of infested plants were higher than uninfested plants. Clearly, the faster breeding rates of the aphids at elevated CO2 caused depletion of N and a resultant deficiency exacerbated chlorosis as well as leaf rolling due to the higher aphid population density under elevated CO2 than at ambient. By 28 days after infestation (DAI), majority of the plants exposed to enriched CO2 treatments had died. A major finding here was thus that although this study demonstrated that elevated CO2 resulted in an increase in biomass, this was detrimentally offset in plants infested by the aphids, with a decline in biomass and loss of functionality leading to plant death at 28DAI. The overriding conclusion from this study is a clear signal that the twin effects of CO2 enrichment (a feature of current climate change) and aphid infestations may precipitate potential grain shortages. A disastrous food security threat looms.
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- Date Issued: 2011
Molecular analysis of genetic diversity in dometicated pigeonpea (Cajanus cajan (L.) Millsp.) and wild relatives
- Authors: Kassa, Mulualem Tamiru
- Date: 2011
- Subjects: Pigeon pea -- Variation Cajanus -- Variation Pigeon pea -- Genetics Cajanus -- Genetics Biodiversity Pigeon pea -- Phylogeny Cajanus -- Phylogeny Plant hybridization Plant diversity Transgenic plants
- Language: English
- Type: Thesis , Doctoral , PhD
- Identifier: vital:4204 , http://hdl.handle.net/10962/d1003773
- Description: Cajanus cajan (L.) Millsp. (Pigeonpea) belongs to the Leguminosae genus Cajanus which is composed of 34 species. Pigeonpea is the only cultivated member of the genus, while the remaining species are wild relatives belonging mainly to the secondary gene pool. DNA sequence data from the nuclear ITS region and the chloroplast trnL-F spacer were utilized to investigate the phylogenetic relationships between Cajanus and five other allied genera in the subtribe Cajaninae. This study revealed the non-monophyly of Cajanus and Rhynchosia and supported the monophyly of Eriosema and Flemingia, but more sampling ,especially from the large genera of Rhynchosia and Eriosema, is recommend to adequately test the hypothesis of generic monophyly. The phylogenetic relationships within the genus Cajanus resolved Cajanus scarabaeoides (L.) Thouars as the most basal species in the Cajanus clade. The study also utilized Single Nucleotide Polymorphism (SNP) markers derived from low copy orthologous genes and genotyped using the high throughput SNP-OPA Illumina golden gate assay. The aim was to understand phylogenetic and domestication history, genetic structure, patterns of genetic diversity, gene flow and historical hybridization between Cajanus cajan (pigeonpea) and wild relatives. The neighbor-joining tree resolved well-supported clusters, which reflect the distinctiveness of species and congruence with their geographical origin. It supported the ITS based phylogeny and resolved C. scarabaeoides as basal to the Cajanus clade. The phylogenetic signal and genetic signatures revealed insights into the domestication history of pigeonpea. Our results supported Cajanus cajanifolius as the presumed progenitor of pigeonpea and we speculate that for pigeonpea there was a single major domestication event in India. Genetic admixture and historical hybridization were evident between pigeonpea and wild relatives. Abundant allelic variation and genetic diversity was found in the wild relatives, with the exception of wild species from Australia, as compared to the domesticated pigeonpea. There was a reduction of about 75% in genetic polymorphism in domesticated pigeonpea as compared to the wild relatives, indicating a severe “domestication bottleneck” during pigeonpea domestication. We discovered SNP markers associated with disease resistance (NBS-LRR) loci. The SNPs were mined in a comparison of BAC-end sequences (BES) of C. cajan and amplicons of the wild species, C. scarabaeoides. A total of ~3000 SNPs were identified from 304 BES. These SNPs could potentially be used in constructing a genetic map and for marker assisted breeding.
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- Date Issued: 2011
The genetic diversity and conservation biology of the rare terrestrial snail genus Prestonella
- Authors: Fearon, Janine Lee
- Date: 2011
- Subjects: Snails -- South Africa , Snails -- Conservation -- South Africa , Snails -- Variation -- South Africa , Biodiversity -- South Africa , Snails -- Genetics -- South Africa , Snails -- Habitat -- South Africa
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4191 , http://hdl.handle.net/10962/d1003760 , Snails -- South Africa , Snails -- Conservation -- South Africa , Snails -- Variation -- South Africa , Biodiversity -- South Africa , Snails -- Genetics -- South Africa , Snails -- Habitat -- South Africa
- Description: Prestonella bowkeri and Prestonella nuptialis are montane specialists endemic to the southern Great Escarpment of South Africa. Phylogeographic analyses of these species based on mitochondrial markers CO1 and 16S reveal extremely high levels of divergence between populations indicating a lack of gene flow between populations. This is not surprising, because P. nuptialis and P. bowkeri have limited dispersal capacity, low vagility, a highly fragmented distribution and are habitat specialists that are restricted to isolated mesic refugia associated with waterfalls and montane seepages. A relaxed Bayesian clock estimate suggests that populations diverged from one another during the mid-late Miocene (12.5-7 MYA) which coincides with the modern trends of seasonal aridity which began during the Miocene. This result should be viewed with caution because the rates used are at best imprecise estimates of mutation rates in snails. There is no clear dichotomy between the two species and P. bowkeri is paraphyletic with respect to P. nuptialis, as a consequence the taxonomy is unclear. Due to the high levels of sequence divergence between populations they may be considered as evolutionary significant units (ESU’s). An assessment of haplotype diversity (h) and nucleotide diversity (π) reveals that populations in the western part of the Great Escarpment are more genetically depauperate than populations in the east. Correlations between genetic diversity and climatic variables show that genetically depauperate populations are found in areas that have lower annual rainfall, less reliable rainfall and higher potential evaporation, all factors associated with a drier, less mesic environment that increases the chances of a population bottleneck. This indicates that a shift towards a more arid environment may be a driver of genetic erosion. Historical climate change may thus have affected the amount and distribution of genetic diversity across the Great Escarpment since the Miocene. This has serious future implications for the survival of Prestonella. With predicted increase in global temperatures, climate change in South Africa is likely to result in range contraction and an eastward range shift for many species in the drier central and western areas (Erasmus et al. 2002) and regions along the Great Escarpment are likely to become more arid. Prestonella populations found living on inselbergs along the Great Escarpment are already restricted to site specific watercourses and seepages. An increase in the periods between stream flow, and increasing rainfall variability and mean annual potential evaporation are likely to have an adverse affect on species living in these habitats, resulting in further bottlenecks and possibly local extinction. An IUCN assessment of P. nuptialis and P. bowkeri suggests that these two species are probably endangered. The issue surrounding the conservation of Prestonella species is that they are threatened by global climate change, which cannot be simply restricted or prevented, which makes dealing with the threat of climate change difficult. Assisted migration (MA) may be considered as a method to prevent possible future extinctions of Prestonella populations, but will only be considered as a last resort. The thermal tolerance (Arrhenius breaking temperature and flat-line temperature) of individual snails from three Prestonella populations (one forest population and two thicket populations) were assessed using infrared sensors that detected changes in heart rate with increasing temperature. The forest population had a significantly lower Arrhenius breaking temperature (ABT) and flat-line temperature (FLT) than the two thicket population (p<0.05). Our results do not show a correlation between upper thermal limits and maximum habitat temperatures or other climatic variables in Prestonella populations. Although no correlation is found between ABT and maximum habitat temperature, it is likely that the differences seen between these populations are due to local micro-climate adaptation. The climatic variables used in this experiment are coarse estimates from GIS data and do not reflect actual microhabitat conditions. Forest environments are less heat stressed than thicket environments due to the forest canopy which may explain the lower ABT and FLT of the forest population.
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- Date Issued: 2011
A systematic study of Berkheya and allies (Compositae)
- Authors: Phaliso, Ntombifikile
- Date: 2013
- Subjects: Compositae -- Africa, Southern , Daisies -- Africa, Southern , Compositae -- Phylogeny -- Africa, Southern , Compositae -- Geographical distribution -- Africa, Southern , Compositae -- Classification -- Africa, Southern , Cladistic analysis
- Language: English
- Type: Thesis , Masters , MSc
- Identifier: vital:4179 , http://hdl.handle.net/10962/d1003054
- Description: Berkheya Ehrh. is a genus of daisies in the tribe Arctotideae, subtribe Gorteriinae with over 80 species, most of which occur in southern Africa. This genus has centres of diversity associated with the montane regions of South Africa, including the Drakensberg Alpine Centre and Mpumalanga escarpment regions. Previous molecular and morphological studies indicate that Berkheya is paraphyletic. I present phylogenies based on nrDNA (ITS; Internal Transcribed Spacer) and cpDNA (psbA-trnH) sequence data analysed with Bayesian Inference and Parsimony. A phylogeny of combined cp- and nrDNA is also presented. These phylogenies are used to assess generic limits and to investigate the biogeographic patterns of Berkheya and its allies. The ITS phylogeny shows five well supported clades of Berkheya, two of which (Clades I and 2) are monophyletic summer rainfall region clades. Clades 3 to 5 are all paraphyletic winter rainfall clades with Cullumia occurring in the third clade, Cuspida occurring in the fourth and Didelta in Clade 5. Both psbA-trnH and combined phylogenies show concordance with the clade distribution shown in the ITS phylogeny. The ITS phylogeny was used to analyse correspondence with Roessler’s (1959) Series. It was found that the phylogeny showed considerable agreement with Roessler’s series, but B. bipinnatifida and B. spinosa of Series Speciosae may require some revision as well as taxa of monotypic series Cruciatae and Angustae. It is suggested that the latter series be merged with Cullumia species to form a single series. Some consideration should be taken to include Didelta species into Series Fruticosae as Didelta occurs in subclade 5b of Clade 5 with other Series Fruticosae taxa. Achene morphology was examined from species from each of the five clades to investigate the relationships of Berkheya and its allies, as well as to determine if there were any consistent achene features for each clade. The structure of surface cells on the fruit, the presence, absence and morphology of twin hairs as well as the structure of the pappus scales were found to be most useful in reflecting phylogenetic relationships within the clades. When compared with the clades of the ITS phylogeny, achene morphology showed consistent characters between taxa occurring in the same clades. As the most comprehensive study involving Berkheya, this phylogenenetic investigation was able to confirm that Berkheya is a paraphyletic genus with Didelta, Cullumia and Cuspida needing to be subsumed into Berkheya. An alternative classification is that taxa of Clade 5 could possibly be erected as an expanded Didelta, separate and sister to Berkheya.
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- Date Issued: 2013