Browsing by Author "Picker, Mike"

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    Bee diversity in Angola and community change along an altitudinal gradient at Serra da Chela (Bruco)
    (2020) Figueira Fernandes Elizalde, Sara Raquel; Picker, Mike; van Noort, Simon
    Insects, including wild bees (Hymenoptera: Anthophila) are exceptional model organisms to assess the effect of climate variation on species richness along altitudinal gradients. Climate variables and weather conditions are of extreme importance for insects particularly since their capacity of body temperature regulation is determined by the ambient temperature. Additionally, bee diversity has proven to be strongly related to the availability of host plants, determinant factors for their presence or absence and both of which are limited at higher altitudes. Therefore, the study of wild bee diversity at various altitudes in the tropics could provide information on possible responses of bee species and communities to climate variations, important to estimate effects of climate change on an important ecosystem service such as pollination. Bees being ecologically important insects with close links to plants, high richness and abundance are well-suited as terrestrial habitat bioindicators. The group is sensitive to environmental disturbances relies upon local plant communities and comprises an assemblage of species with varying social structure, nesting guilds and other life history traits. Additionally, bees are likely more susceptible to negative effects of small effective population size. The life history traits determine the individual and community response to environmental changes. Records from the literature revealed a collector and seasonal bias, with greater effort applied around big cities or specific collecting locations and mainly in the wet season. A preliminary checklist of bees of Angola was created and comprises 209 bee species from 47 genera and five families, but a major proportion of the country's area remains to be surveyed. A national inventory of Angolan bees is proposed, making use of standardized methods and sampling either one quarter degree cell or half degree cells, ideally in both dry and rainy seasons. Wild bee communities were sampled along an altitudinal gradient (760-1651 m.a.s.l) in the biodiversity rich and critically endangered Angolan escarpment. Pan traps, malaise traps and sweep netting were used at twelve sampling points, with an average of 70 m difference in altitude between points. Sweep netting proved to be the most efficient technique. Overall, 845 individuals were collected, representing 51 identified species, 34 genera and five bee families. Contrary to the trends observed in other studies in the tropics, a consistent increase in bee diversity (carried out at genera level) with increasing altitude, from the lower altitude (H'=2,14) to the higher altitude of the gradient (H'=2,26) was found. In addition, community structure differed along the gradient, with distinctive communities in low elevation sites being dominated by Braunsapis, Ceratina, Hypotrigona and Anthidiellum, and high elevation sites the distinctive communities were dominated by Amegilla, Macrogalea, Patellapis and Xylocopa. This result might be consistent with findings from studies of other taxa that attribute to the Angolan escarpment an importance as a centre of endemism and speciation. The results from this study are possibly explained by a combination of factors where the exceptional geomorphology and landscape shape the (direct) influence of environmental variables such as temperature and precipitation on the vegetation communities along the gradient therefore (indirectly) affecting bee community assemblages, particularly for the more specialized bee genera and species. Limited research has been done on the variation of bee body size along altitudinal gradients, but the few studies that have been carried out indicate that future changes (warming) in climatic conditions will most probably alter bees body size (by reduction), consequently affecting their thermoregulatory capacity and, at a larger scale, the overall patterns of community assembly. Along the tropical altitudinal gradient of this study, bee body size was found to increase with altitude by 58% (mean length at lower altitude = 5.06mm against mean = 7.99mm at higher altitude elevation sites) at the community level but also at the intra-specific level, with Macrogalea candida increasing 4% in size between the lower altitude and summit of the transect (mean length at lower altitude = 8.76mm against mean = 9.12mm at higher altitude elevation sites), suggesting that the fairly small temperature gradient along the transect was sufficient to select for body size – either directly, but more likely through multiple avenues, including indirect effects such as changes in rainfall, plant community composition and plant phenology. This result constitutes, to my best knowledge, the first demonstration of Bergmann's rule applicability at different levels of biotic organization of bee communities in the tropical region. Effective conservation planning is highly dependent on robust, spatially explicit biodiversity data. The generation of comprehensive insect profiles through long term monitoring studies at the national level can identify areas with high species turnover and endemism – patterns that could be missed if only vertebrate data were considered. In under-developed countries like Angola, where a poorly documented but highly rich biodiversity is severely threatened by unregulated land use, and research is hampered by financial constraints and lack of human resources, the combined use of indicator taxa for both terrestrial (bees) and freshwater (Odonata) environments might be a reasonable surrogate for total biodiversity status assessments. The results from this study highlight the need for long term monitoring to efficiently assess bee diversity, especially in critically endangered landscapes where anthropogenic pressures are high.
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    Conservation and monitoring of invertebrates in terrestrial protected areas
    (2011) McGeoch, Melodie A; Sithole, Hendrik; Samways, Michael J; Simaika, John P; Pryke, James S; Picker, Mike; Uys, Charmaine; Armstrong, Adrian J; Dippenaar- Schoeman, Ansie S; Engelbrecht, Ian A; Braschler, Brigitte; Hamer, Michelle
    Invertebrates constitute a substantial proportion of terrestrial and freshwater biodiversity and are critical to ecosystem function. However, their inclusion in biodiversity monitoring and conservation planning and management has lagged behind better-known, more widely appreciated taxa. Significant progress in invertebrate surveys, systematics and bioindication, both globally and locally, means that their use in biodiversity monitoring and conservation is becoming increasingly feasible. Here we outline challenges and solutions to the integration of invertebrates into biodiversity management objectives and monitoring in protected areas in South Africa. We show that such integration is relevant and possible, and assess the relative suitability of seven key taxa in this context. Finally, we outline a series of recommendations for mainstreaming invertebrates in conservation planning, surveys and monitoring in and around protected areas. Conservation implications: Invertebrates constitute a substantial and functionally significant component of terrestrial biodiversity and are valuable indicators of environmental condition. Although consideration of invertebrates has historically been neglected in conservation planning and management, substantial progress with surveys, systematics and bioindication means that it is now both feasible and advisable to incorporate them into protected area monitoring activities.
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    Dietary shifts in pollen-feeding lacewings (Nemopteridae) in relation to vegetation, biome and phylogeny
    (2014) Chirango, Yolanda; Gillson , Lindsey; Picker, Mike
    The spoon-winged and threadwinged lacewings are a diverse nemopterid family that have flourished in the winter rainfall region of South Africa. Their diversity is thought to be linked to the radiation of Aizoaceae, a member of the Ruchioideae subfamily that radiated at the same time as the recently diversified nemopterids in the Succulent Karoo. Phylogenetic data supported this assertion, and seperated the family into two distinct lineages, a recently diversified Aizoaceae-dependent Succulent Karoo lineage and a basal Aizoaceae-independent Fynbos lineage. This study aimed to determine if the nemopterid diet is phylogenetically contrained or if diet was mearely a reflection of plant availability. This was investigated by carrying out a dietary analysis of the gut contents of nemopterids from different biomes, vegetation and localities. It was hypothesised that diet would be phylogenetically constrained and dietary grouping would reflect phylogeny. In addition, the derived nemopterid lineage thought to have co-evolved with Aizoaceae, (Palmipenna, Nemopterella, Nemia, and Knersvlaktia) would reflect this in its diet. The older lineage (Nemeura, Sicyoptera, Semirhynchia, and Derhynchia) was hypothesised to have its phylogenetic grouping reflected in its diet by having very little to no Aizoaceae in its diet. The results showed that dietary groupings did not reflect phylogenetic groupings and dietary similarities were shared across most genera, including subfamilies, with Lauhervasia, a member of the Crocinae subfamily sharing 80% of its pollen sources with Semirhynchia, of the Nemopterinae subfamily. Aizoaceae reliance was only consistantly present in Nemia, which belonged to the phylogenetic lineage expected to rely on Aizoacea. All the members of the phylogenetic lineage not expected to rely on Aizoaceae, did not have any Aizoaceae in their diet. The diet of the nemopterids was very diverse across all vegetation types and biomes. The study suggests that spoon-winged and threadwinged lacewings are generalist pollinators and recent diversification was most likely linked to their ability to utilise the large range of available resources and not linked to a single plant family that radiated around the same time.
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    The effects of heuweltjies and Microhodotermes viator (Isoptera: Hodotermitidae) on invertebrate assemblages and species turnover in the succulent Karoo, Western Cape
    (2014) Cornell, Gabriel Lyle; Picker, Mike; Colville, Jonathan
    Species turnover is a measure of a diversity that attempts to quantify the change in species composition along a spatial, temporal or environmental gradient. One such environmental gradient that has been shown to affect species turnover is local edaphic variation. This is seen in the Western Cape Province of South Africa, where the unique edaphic character of large earth mounds, known as heuweltjies, support distinct plant communities. The aim of this study is to assess whether these mounds, and the termite Microhodotermes viator commonly associated with them, also support distinct invertebrate communities, thereby contributing to invertebrate species turnover in the region. Pitfall and emergence traps were set on heuweltjies and in the surrounding matrix in the Karoo Desert National Botanical Gardens, Worcester, Western Cape Province. On- and off-mound community contrasts were assessed by means of a cluster analysis, and species turnover was measured using the Jaccard distance. Invertebrates were more abundant on the heuweltjies, which also had distinct communities when compared to the matrix. Spiders (Aranaea) were more abundant on the heuweltjies, as were in the invertebrates emerging from the frass, suggesting a trophic cascade. Invertebrates commonly associated with M. viator were found more commonly on the heuweltjies. The Jaccard distances indicated that environmental homogenisation of the heuweltjies resulted in homogenisation of the on-mound invertebrate communities. Heuweltjie soil enrichment was most similar to that of termite frass when compared to the matrix, supporting a termite origin for the heuweltjies.
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    Effects of water temperature on life history traits of selected South African Aquatic insects: implications for the ecological reserve
    (2014) Ross-Gillespie, Vere; Dallas, Helen Fiona; Day, Jenny; Picker, Mike
    Life-history studies have informed all areas of aquatic ecological research, whilst also providing information relevant for conservation and management of aquatic systems. Given the large research gap that has existed in this regard for Southern Hemisphere lotic systems, there has been an urgent need to gather such data if effective management policies are to be implemented regionally, especially in the face of ongoing development, anthropogenic impacts, and global climate change. Furthermore, there has been a growing awareness of the need to incorporate thermal guidelines into legislation regarding environmental flows and associated water management plans. In South Africa radical new legislation introduced in 1996 resulted in rivers and aquatic ecosystems being given a right to water of their own- essentially environmental flows, required to protect the aquatic ecosystems associated with the water resource, that are determined separately for all or part of any significant water resource. This water, including both the quantity and quality, is referred to as the "Ecological Reserve." Baseline information on the relationship between temperature and life-history patterns of aquatic insects is required to inform the incorporation of thermal guidelines in the Ecological Reserve determination process. Assuming such information can be gathered, a problem arises as to how the data can be interpreted and incorporated into management guidelines. For instance if representatives of widespread species occurring throughout a country are collected from a single location (say perhaps a single province in South Africa) and then analysed in terms of their thermal limits for growth – would these limits hold true for that same species where it occurs elsewhere? Intra-specific variability, cryptic species and broader phylogenetic constraints all influence the thermal limits of species and need to be considered when examining thermal influences on life-history patterns. This thesis aimed to test the overarching hypothesis that while the life-history traits of aquatic insects could be constrained to some degree by their evolutionary history, they would also be impacted by thermal and hydrological regimes, inducing a degree of plasticity in their life cycles. This hypothesis was tested by examining the key life-history traits of three representative taxa of aquatic insect, namely Lestagella penicillata (Ephemeroptera), Aphanicercella spp. (Plecoptera) and Chimarra ambulans (Trichoptera), and how they are driven by environmental and genetic factors in six rivers situated in the south-western Cape Province of South Africa.
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    Host associations and pollution responses of ciliate epibionts of macroinvertebrates in the six rivers in the Western Cape Province of South Africa
    (2012) Ukomadu, Nwamaka Mary-Immaculata; Picker, Mike; Roets, F
    This study is the first documentation of ciliate epibiont-host associations in the Western Cape Province of South Africa. Benthic macroinvertebrates were sampled from six rivers in the Western Cape Province (Wolwekloof, Wit, Rooielskloof, Molenaars, Elandspad and Eerste) to determine epibiotic prevalence and to explore relationships between prevalence and host abundance. Ciliate morphology and 18S rDNA and ITS region sequence data were used to identify the different taxa present, and attachment preferences of epibiont colonies for host body part were determined. The response of ciliate epibionts to water pollution along a pollution gradient in the Eerste River was examined to assess their potential as bioindicators of water pollution.
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    The impact of pine plantations and alien invertebrates on native forest and fynbos invertebrate communities in Table Mountain National Park
    (2012) Uys, Charmaine Janet; Picker, Mike; Griffiths, Charles L
    While the Cape Peninsula (South Africa) is renowned for its exceptional plant and invertebrate diversity and endemism, extensive alien plant invasions and exotic pine plantations threaten and reduce native species richness. This study frames invasion ecology theory in a conservation context, and examines the impact of planting and felling pine on litter invertebrate communities, by comparing invertebrate diversity between pine plantations and native vegetation. Impacts of the worst invasive alien invertebrate (Argentine ant, Linepithema humile) and other alien invertebrate species are investigated. This is one of the first attempts to inventory and quantify impacts of non-ant alien invertebrates in Table Mountain National Park. The entire ground-dwelling invertebrate community was sampled at 31 sites in summer 2008/2009, using soil cores, leaf litter samples, pitfall traps, sugar-baited ant traps and decayed logs. A total of 112 404 individuals, representing 728 species (10 classes and 38 orders), including nine Cape Peninsula endemic and 19 alien species, was collected. Pine plantations supported lower species richness and abundance, and different community assemblages, compared to Afrotemperate forest, but similar species richness to fynbos. This supports previous local studies and global trends. Pine plantations shared fewer species with fynbos than forest, and negatively affect fynbos-specialist invertebrates, because afforestation reduced available fynbos habitat. Alien species richness was similar across habitats. Argentine ants, like most other alien species identified, were present in all habitats. The impact of Argentine ant invasion on native ant communities was evaluated using species richness and community composition analyses, species co-occurrence patterns (C-score), and the functional group approach. The comparative approach adopted provided no evidence for displacement, impoverishment, or community disassembly. No clear impacts of the 18 non-ant alien species on the abundance, species richness, or community composition of corresponding native taxa were detected. Disturbance history offers a more parsimonious explanation for the trends observed, particularly in fynbos. However, carnivorous molluscs require careful monitoring, given their abundance and known impacts elsewhere. Using a reiterative process and IndVal, two ant species (Pheidole capensis and Camponotus bertolinii) were selected as ecological indicators of restoration progress in fynbos following clear-felling of pine. Ants similarly have application for monitoring in other Mediterranean-type ecosystems impacted by invasive pines.
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    Impact of the invasive ant Linepithema humile on native ant assemblages on the western slopes of Table Mountain and implications for ant-butterfly associations
    (2011) Krahner, André; Picker, Mike
    The Argentine Ant, Linepithema humile (Hymenoptera: Formicidae), is one of the world's most successful invasive species and invades undisturbed Fynbos habitats in South Africa, displacing native arthropod species and affecting interspecific associations. In order to assess the impact of Li. humile on native ant assemblages and associations between ants and myrmecophilous butterflies (Lepidoptera: Lycaenidae) on the western slopes of Table Mountain (Cape Town, South Africa), adult butterfly density was scored and distribution of food plants were assessed at two sites.
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    Life cycle and host preferences in the Agapanthus borer (Neuranethes spodopterodes)
    (2013) Dabee, Vidushi Prema; Picker, Mike
    The species Neuranethes spodopterodes is a pest of the Agapanthus species. The larva feeds gregariously on the leaves and rhizomes and cause extensive damage to the plant. This study shows the N.spodopterodes have 6 larval instars. The use of the head capsule width as a morphometric parameter and applying it to Dyar's rule gives significant results which allow for adequate determination of the larval instar. The Agapanthus borer has a life cycle that last approximately 84 days. Some species of Agapanthus are the preferred host plant for oviposition by the female N.spodopterodes. Agapanthus inapertus, Agapanthus caulescens and Agapanthus praecox are the most infested with the Agapanthus borer eggs. Leaf sizes do not appear to be a factor that influences the female choice. There appears to be no preference from the larva during feeding. The larva fed equally on all the six Agapanthus species including A. africanus (p>0.05). This shows that the chemical composition of these species is closely related. Since the larva has no feeding preference, this reinforces the fact that it is the female moth that chooses the host plant and that it abides with preference-performance hypothesis. Since A. africanus is subjected to feeding by the larva under laboratory conditions, it could potential imply that in the event of a range shift by the gravid female, that this species of plant is at risk of extinction. The presence of a parasitoid wasp, Trichogramma in the egg of N. spodopterodes and that the level of parasitism is about 86% suggests that this parasitoid could potentially be used as a biological control agent of the Agapanthus borer.
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    Life cycle and host preferences in the Agapanthus borer (Neuranethes spodopterodes)
    (2013) Vidushi Prema Dabee; Picker, Mike
    The species Neuranethes spodopterodes is a pest of the Agapanthus species. The larva feeds gregariously on the leaves and rhizomes and cause extensive damage to the plant. This study shows the N.spodopterodes have 6 larval instars. The use of the head capsule width as a morphometric parameter and applying it to Dyar‟s rule gives significant results which allow for adequate determination of the larval instar. The Agapanthus borer has a life cycle that last approximately 84 days. Some species of Agapanthus are the preferred host plant for oviposition by the female N.spodopterodes. Agapanthus inapertus, Agapanthus caulescens and Agapanthus praecox are the most infested with the Agapanthus borer eggs. Leaf sizes do not appear to be a factor that influences the female choice. There appears to be no preference from the larva during feeding. The larva fed equally on all the six Agapanthus species including A. africanus (p>0.05). This shows that the chemical composition of these species is closely related. Since the larva has no feeding preference, this reinforces the fact that it is the female moth that chooses the host plant and that it abides with preference-performance hypothesis. Since A. africanus is subjected to feeding by the larva under laboratory conditions, it could potential imply that in the event of a range shift by the gravid female, that this species of plant is at risk of extinction. The presence of a parasitoid wasp, Trichogramma in the egg of N. spodopterodes and that the level of parasitism is about 86% suggests that this parasitoid could potentially be used as a biological control agent of the Agapanthus borer.
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    Phylogenetic relationships among beetles within the genus Onymacris (Coleoptera : Tenebrionidae) : a phenetic versus cladistic approach
    (1986) Atmore, John David; Crowe, Timothy M; Picker, Mike
    Phylogenetic relationships among species within the beetle genus Onymacris (Coleoptera Tenebrionidae) are identified using phenetic and cladistic approaches. Phylogenetic results from cladistic analyses proved to be more robust than those derived with phenetic approaches. However, phenetic analyses proved to be useful in identifying possible interspecific hybridization. Two monophyletic subgenera are recognized. The subgenus Melanonymacris comprises O. lobicollis, O. rugatipennis, O. paiva, O. boschimana, O. multistriata, O. hottentota and O. plana, all of Which have black elytra. The subgenus Onymacris comprises O. langi, O. marginipennis, O. brainei, O. candidipennis and O. bicolor, all of which have pale-coloured elytra, and two species with black, 'bullet-shaped' elytra, O. laeviceps and O. unguicularis. The resulting cladogram and the characters and synapomorphies underpinning it are compared with those from an independently conducted study (Penrith 1984). The implications of the cladogram are discussed in the lignt of the tenets of vicariance biogeography and the constraints of adaptation to the extreme desert environment.
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    Sociogenetic investigation of the southern harvester termite, Microhodotermes viator, via genetic and behavioural bioassays
    (2014) Muna, Natashia; O'Ryan, Colleen; Picker, Mike
    This thesis presents the first investigation of the population structure of the southern harvester termite, Microhodotermes viator (Family: Hodotermitidae), by assessing the genetic state and behavioural interactions within and between twelve colonies, from four areas across the Western Cape of South Africa. This study also critically debates the relationship between M. viator and heuweltjies (small Mima-like earth mounds), with regards to their origins and age. By critically analysing what is known, and debating the merits and shortcomings of various published hypotheses, this thesis concludes that heuweltjies are unequivocally attributable to the constructions and foraging activities of M. viator. However, the age and longevity of heuweltjies remains contentious. Several studies have attempted to ascertain age, using radiometric carbon dating on the basal calcrete layer found below mature heuweltjies, but there is disparity between results, primarily due to the challenges associated with dating calcrete. Therefore, an alternative method better equipped to mitigate these challenges, such as U-series isochron dating, is suggested for future research.
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    Stream invertebrates and water temperature : evaluating thermal tolerances in the Cape floristic region (South Africa) - implications of climate change
    (2009) Ketley, Zoma Anne; Picker, Mike; Reed, Cecile C; Dallas, Helen Fiona
    Temperature is an important environmental variable for aquatic invertebrates as it affects their development, reproduction and survival. Temperature also affects the abundance and distribution of individuals in a stream or river. Stream temperatures are affected by human impacts which include not only impacts such as pollution, abstraction of water and the removal of riparian vegetation, but also the affects of climate change. In the Western Cape Province, South Africa, it is predicted that air temperatures will increase and winter rainfall will decrease. This in turn will affect water availability and water temperatures in streams and rivers. Thermally sensitive species are threatened by increases in water temperature, but currently very little information exists on the thermal tolerances of aquatic invertebrates in South Africa. In order to rectify this problem baseline data on thermal tolerances of aquatic species needs to be collected, together with stream temperature and associated invertebrate community data. An attempt was made to collect some of these much needed data in the Western Cape Province. Two methods, namely Critical Thermal Maxima (CTM) and LTâ‚…â‚€ experiments, were used to determine the thermal tolerances for a range of aquatic insect nymph species from the southwest fynbos bioregion and the south coast fynbos bioregion. The results from the experiments provided information on the relative thermal sensitivities of the species. Overall Aphanicerca capensis (form C and undescribed form), Notonemouridae ranked as the most thermally sensitive for both experiments. The A. capensis species complex (and possible other notonemourid stoneflies) may potentially be used as an indicator of changing stream temperatures in the Western Cape Province. To rapidly determine thermal sensitivities the CTM experiments are recommended rather than the more time consuming LTâ‚…â‚€ experiments as the relative thermal tolerance for the species tested ranked the same for both experiments. It is suggested that LTâ‚…â‚€ experiments of longer duration be investigated in order to compare the experiments to naturally-occurring thermal stress. Stream temperature and community composition data were collected from Window Gorge Stream, on Table Mountain, to provide baseline data for future monitoring and understanding of potential changes in thermal profiles. Temperature loggers were placed at six sites along the stream. Stream temperatures were fairly low but the stream ran dry during the late summer months (February through to April/May). From the community composition data collected the highest diversity was found during the winter months, as expected. The community composition did change down the length of the stream, with the species composition found near the source being quite different to that of the species composition found lower down the mountain. Temperature and associated oxygen saturation were two important variables related to the community composition down the length of the stream. It is important that experimental data be combined with field data, enabling field sampling to focus on the collection of information on the abundance of the thermally sensitive species (e.g. A. capensis species complex). Recorded stream temperatures also provide reference conditions for the species tested in the laboratory. Climate change is likely to have an affect not only on stream temperatures but also on water availability, which will both influence stream communities and ecosystems and it is important to understand what these potential effects might be.
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    Systematics of the Notonemouridae (Plecoptera) of southern Africa
    (2008) Stevens, Duncan Mark; Picker, Mike; Bishop, Jacqui
    The broad aims of this research, following the establishment of a firm taxonomic base for the southern African Notonemouridae, were to investigate species boundaries and to infer phylogenetic relationships in the Aphanicerca capensis Tillyard species complex using morphological, behavioural and molecular data (mtDNA), and to model historical biogeographic patterns and drivers of cladogenesis. Additionalaims included an evaluation of the cytochrome oxidase subunit I gene as a molecular barcode in the Notonemouridae, a test of the monophyly of the genera, the construction of a phylogeny for the southern African Notonemouridae and the identification of clade synapomorphies.
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    Understanding the evolutionary radiation of the megadiverse monkey beetle fauna (Scarabaeidae: Hopliini) of South Africa
    (2009) Colville, Jonathan F; Picker, Mike; Cowling, Richard M
    Most HIV vaccines currently in development aim to protect people from infection or disease by eliciting strong anti-HIV cytotoxic T lymphocyte (CTL) responses. Evolved evasion mutations that undermine host immune responses pose a major challenge to the development of such vaccines. Understanding the mechanisms that selectively favour the emergence of CTL evasion mutations in vivo and the impact of these mutations on both disease progression and long-term HIV evolution will not only contribute to our understanding of HIV pathogenesis, but will also inform vaccine design strategies. This study aimed at investigating CTL escape mutations in HIV-1 Gag and Nef, during the acute and early phases of infection and the impact of these mutations on subsequent disease progression in a cohort of recently HIV-1 subtype C infected females. Of 36 women recruited into the study within 12 weeks of infection (median 6 weeks) and followed for six months, 32 were infected with single viruses. Two participants were infected with epidemiologically unlinked viruses (dual infection), and in a further two individuals the viruses were highly divergent suggestive of dual infection and/or recombination. These individuals were excluded from further analysis as it was difficult to predict CTL escape due to high degrees of diversity between sequences. In the remaining 32 study participants, there was a high frequency of CTL escape with putative escape mutations identified in 21 of 32 individuals (66%). Twelve of these 21 (33%) harboured viruses which developed escape mutations in Gag, and 17 (53%) developed escape mutations in Nef. In the conserved structural protein, p24, potential reversion mutations were more frequent than potential escape mutations. During the first six months of infection whereas potential reversion mutations occurred at low entropy sites, potential escape mutations occurred at high entropy sites. Although there was no detectable association between the timing of escape mutations and disease progression, there was an association between the degree of deviation of the p24 sequence from the subtype-C population consensus (a measure of escape mutation load) and CD4+ counts. Analysis of the earliest sampled viruses from HLA-B*57/B*5801 negative study participants for viral genetic markers associated with disease progression identified two iv polymorphisms, A146X (n = 9) and T242N (n =6), that were associated with improved viral control. The polymorphisms are well-known escape mutations in HLAB* 57/B*5801 restricted epitopes. This suggested transmission of these variants from individuals carrying these alleles. Further evidence that viruses carrying the T242N and/or A146X mutations had been previously passaged through B*57/B*5801 positive individuals came from the fact that the observed T242N mutations reverted to wild type during follow-up. There was no significant change in viral load and CD4+ counts upon reversion of the T242N mutations. In vitro replication assays using chimeric viruses containing gag sequences from one of participants showed that the virus harbouring the T242N mutation was fitter than that carrying the reversion mutation. These viruses harboured other T242N associated compensatory mutations suggesting that these compensatory mutations may themselves carry a fitness cost in the absence of the T242N mutation. This suggests that there possibly exist networks of B*57/B*5801 associated mutations and that reversion of some of these mutations in isolation does not necessarily restore viral fitness. Lastly, the kinetics of CTL escape in HLA-B*5801 positive participants (n = 6) and the impact of escape on disease progression was investigated. CTL escape within B *5801 positive individuals was found to predominantly occur within the TW10 in Gag (n = 4) and KAF9 in Nef (n = 6) epitopes. The emergence of the T242N mutation in TW10 was always preceded by mutations elsewhere in the epitope and was associated with the occurrence of previously described compensatory mutation upstream of the epitope. The targeting of TW10 and the emergence of T242N escape mutations were associated with higher CD4+ counts at 12 months postinfection in the B*5801 positive individuals (p = 0.0231 and p = 0.0282, respectively). Independent of host HLA genotypes, the presence of the A146X and T242X mutations was associated with higher CD4+ counts (p = 0.0495). This study provides some useful insights into HIV-1 subtype C pathogenesis. The notion that CTL escape mutations do not invariably result in less fit viruses is evidenced by the observation that escape was not obviously associated with disease progression in this cohort, while escape mutations in the Gag p24 region within B*5801 positive individuals v in particular, was associated with improved viral control. There is therefore evidently a complex interaction between escape and compensatory mutations and further work is required to identify the impact of compensatory mutations on viral fitness. Overall, this study provides further evidence that vaccines need to elicit responses that specifically target the functionally constrained regions of the HIV proteome.