Browsing by Author "Colville, Jonathan F"
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- ItemOpen AccessBehavioural, microhabitat, and phylogenetic dimensions of intrasexual contest competition in combatant monkey beetles (Scarabaeidae: Hopliini)(2021) Rink, Ariella N; Altwegg, Res; Colville, Jonathan F; Bowie, Rauri C KThe importance of sexual selection as a driver of evolution, from microevolution to speciation, has overwhelmingly been studied in the context of female choice, but there is evidence that male-male competition can also drive evolution. Recent reviews of the intrasexual competition literature have developed several hypotheses of weapon divergence in both allopatry and sympatry and have suggested means by which weapon divergence may cause reproductive isolation and speciation, both alone and together with mate choice and ecological selection. Here, I assess the role of sexual selection, in the context of environmental variation at the level of the contest substrate and the developmental environment, in contributing to microevolution within the monkey beetles (Coleoptera: Scarabaeidae: Hopliini), a taxonomically and phenotypically diverse group of pollinating insects in the Greater Cape Floristic Region (GCFR) that shows a high degree of sexual dimorphism and mating behaviour driven by male-male competition. I build on previous observations of hind leg use in intrasexual male-male contest for reproductive access to females by showing that, in Heterochelus chiragricus, contests occur in the context of a significantly maleskewed sex-ratio and consist of vigorous wrestling and pushing between two males on the flower heads occupied by embedded, feeding females, who apparently exert no mate choice. Contest outcomes are influenced by hind femur size and residency effects, and I apply hypotheses informed by evolutionary game theory to assess how males make decisions regarding persistence versus retreat. I proceed to assess the evidence for the ‘divergent fighting contexts' hypothesis which predicts weapon divergence driven by intrasexual contest competition in the context of variation in the contest substrate. I find that hind leg size in another combatant monkey beetle, the species complex Scelophysa trimeni, varies across gradients of flower size among several spatially distributed populations, suggesting that variation in flower size (the contest substrate) mediates selection for weapon morphologies that maximise performance under different fighting styles necessitated by differences in the contest substrate. I also find that male elytral colour varies both across gradients in the developmental environment and with variation in flower colour, suggesting that this trait may function as an honest signal of male fitness, but also that it may be under selection to maximise signal transmission against variable backgrounds of contest substrates. Finally, I quantify the extent to which integration, modularity, multivariate allometry, and phylogenetic effects influence the evolutionary lability of male monkey beetle's hind legs, and so mediate the pace of their evolutionary diversification in response to these varying contest substrates. My findings support a two-module pattern of modularity at both static and evolutionary levels, and I find that allometric scaling relationships are conserved within S. trimeni. These findings indicate that monkey beetle weapons are relatively unconstrained in their evolutionary diversification across divergent fighting substrates. I conclude by discussing these findings within the broader field of sexual selection and monkey beetle ecology and suggest directions for further work. The findings presented here support a role for sexual selection, interacting with variation in the flower contest substrate, as being an important driver of the diversification of monkey beetles in the GCFR.
- ItemOpen AccessOptimising regionalisation techniques: identifying centres of endemism in the extraordinarily endemic-rich Cape Floristic Region(Public Library of Science, 2015) Bradshaw, Peter L; Colville, Jonathan F; Linder, H PeterWe used a very large dataset (>40% of all species) from the endemic-rich Cape Floristic Region (CFR) to explore the impact of different weighting techniques, coefficients to calculate similarity among the cells, and clustering approaches on biogeographical regionalisation. The results were used to revise the biogeographical subdivision of the CFR. We show that weighted data (down-weighting widespread species), similarity calculated using Kulczinsky's second measure, and clustering using UPGMA resulted in the optimal classification. This maximized the number of endemic species, the number of centres recognized, and operational geographic units assigned to centres of endemism (CoEs). We developed a dendrogram branch order cut-off (BOC) method to locate the optimal cut-off points on the dendrogram to define candidate clusters. Kulczinsky's second measure dendrograms were combined using consensus, identifying areas of conflict which could be due to biotic element overlap or transitional areas. Post-clustering GIS manipulation substantially enhanced the endemic composition and geographic size of candidate CoEs. Although there was broad spatial congruence with previous phytogeographic studies, our techniques allowed for the recovery of additional phytogeographic detail not previously described for the CFR.
- ItemOpen AccessPollination ecology of Mesembs(2002) Scodanibbio, Lucia; Bond, William J; Colville, Jonathan FMesembryanthemaceae is one of the main plant families in the Succulent Karoo biome of South Africa. While its pollination ecology still remains largely unstudied, the system is thought to be overall generalised. This study sought to verify whether Mesemb species flowering during September and October in Vrolijkheit Nature Reserve have generalised or specialised pollination interactions. The determinants of insect choice to a particular plant species were investigated and possible mechanisms adopted by different plant species to prevent interspecific pollen transfer were explored. The system was found to have a generalisation level of 24.7%, indicating that one of four possible interactions actually took place. A relatively high degree of overlap in insect visitors was found between the three white-flowered species (Mesemhryanthemum longistylum, Phylloholus grossus and P. splendens). Colour was one of the main determinants of insect choice, whereby Drosanthemurn speciosum, the only red-flowered species in the study showed the highest degree of specialisation. Both scent and nectar production were relatively important in attracting flower visitors. Seasonality in flowering appeared to be a very important mechanism used to reduce overlap in insect visitors, especially among intrageneric species and those that had flowers of the same colour. Daily patterns in scent and nectar production also appeared to play a role in lowering pollinator-sharing. Given the general floral structure of most Mesemb flowers, these mechanisms are likely to be very important in contributing to species reproductive isolation and the low occurrence of hybrids recorded in natural conditions.
- ItemOpen AccessRoles of spatial scale and rarity on the relationship between butterfly species richness and human density in South Africa(Public Library of Science, 2015) Mecenero, Silvia; Altwegg, Res; Colville, Jonathan F; Beale, Colin MWildlife and humans tend to prefer the same productive environments, yet high human densities often lead to reduced biodiversity. Species richness is often positively correlated with human population density at broad scales, but this correlation could also be caused by unequal sampling effort leading to higher species tallies in areas of dense human activity. We examined the relationships between butterfly species richness and human population density at five spatial resolutions ranging from 2' to 60' across South Africa. We used atlas-type data and spatial interpolation techniques aimed at reducing the effect of unequal spatial sampling. Our results confirm the general positive correlation between total species richness and human population density. Contrary to our expectations, the strength of this positive correlation did not weaken at finer spatial resolutions. The patterns observed using total species richness were driven mostly by common species. The richness of threatened and restricted range species was not correlated to human population density. None of the correlations we examined were particularly strong, with much unexplained variance remaining, suggesting that the overlap between butterflies and humans is not strong compared to other factors not accounted for in our analyses. Special consideration needs to be made regarding conservation goals and variables used when investigating the overlap between species and humans for biodiversity conservation.
- ItemOpen AccessUnderstanding the evolutionary radiation of the megadiverse monkey beetle fauna (Scarabaeidae: Hopliini) of South Africa(2009) Colville, Jonathan F; Picker, Mike; Cowling, Richard MMost 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.