Jessica M. da Silva

Slow but tenacious: an analysis of running and gripping performance in chameleons.

SUMMARY Chameleons are highly specialized and mostly arboreal lizards characterized by a suite of derived characters. The grasping feet and tail are thought to be related to the arboreal lifestyle of chameleons, yet specializations for grasping are thought to exhibit a trade-off with running ability. Indeed, previous studies have demonstrated a trade-off between running and clinging performance, with faster species being poorer clingers. Here we investigate the presence of trade-offs by measuring running and grasping performance in four species of chameleon belonging to two different clades (Chamaeleo and Bradypodion). Within each clade we selected a largely terrestrial species and a more arboreal species to test whether morphology and performance are related to habitat use. Our results show that habitat drives the evolution of morphology and performance but that some of these effects are specific to each clade. Terrestrial species in both clades show poorer grasping performance than more arboreal species and have smaller hands. Moreover, hand size best predicts gripping performance, suggesting that habitat use drives the evolution of hand morphology through its effects on performance. Arboreal species also had longer tails and better tail gripping performance. No differences in sprint speed were observed between the two Chamaeleo species. Within Bradypodion, differences in sprint speed were significant after correcting for body size, yet the arboreal species were both better sprinters and had greater clinging strength. These results suggest that previously documented trade-offs may have been caused by differences between clades (i.e. a phylogenetic effect) rather than by design conflicts between running and gripping per se.

Linking microhabitat structure, morphology and locomotor performance traits in a recent radiation of dwarf chameleons

Summary 1. Evidence that morphological traits associated with particular environments are functionally adapted to those environments is a key component to determining the adaptive nature of radiations. Adaptation is often measured by testing how organisms perform in diverse habitats, with performance traits associated with locomotion thought to be among the most ecologically relevant. 2. We therefore explored whether there are relationships between morphology, locomotor performance traits (sprint speed, forefoot and tail grip strength on broad and narrow dowels) and microhabitat use in five phenotypic forms of a recent radiation of dwarf chameleon – the Bradypodion melanocephalum–Bradypodion thamnobates species complex – to determine whether morphological differences previously identified between the forms are associated with functional adaptations to their respective habitats, which can be broadly categorized as open or closed-canopy vegetation. 3. The results showed significant differences in both absolute and relative performance values between the phenotypic forms. Absolute performance suggests there are two phenotypic groups – strong (B. thamnobates and Type B) and weak (B. melanocephalum and Types A and C). Relative performance differences highlighted the significance of forefoot grip strength among these chameleons, with the closed-canopy forms (B. thamnobates, Types B and C) exceeding their open-canopy counterparts (B. melanocephalum, Type A). Little to no differences were detected between forms with respect to sprint speed and tail strength. These results indicate that strong selection is acting upon forefoot grip strength and has resulted in morphological adaptations that enable each phenotypic form to conform with the demands of its habitat. 4. This study provides evidence for the parallel evolution of forefoot grip strength among dwarf chameleons, consistent with the recognition of open and closed-canopy ecomorphs within the genus Bradypodion.

Sexual Dimorphism in Bite Performance Drives Morphological Variation in Chameleons

Phenotypic performance in different environments is central to understanding the evolutionary and ecological processes that drive adaptive divergence and, ultimately, speciation. Because habitat structure can affect an animal’s foraging behaviour, anti-predator defences, and communication behaviour, it can influence both natural and sexual selection pressures. These selective pressures, in turn, act upon morphological traits to maximize an animal’s performance. For performance traits involved in both social and ecological activities, such as bite force, natural and sexual selection often interact in complex ways, providing an opportunity to understand the adaptive significance of morphological variation with respect to habitat. Dwarf chameleons within the Bradypodion melanocephalum-Bradypodion thamnobates species complex have multiple phenotypic forms, each with a specific head morphology that could reflect its use of either open- or closed-canopy habitats. To determine whether these morphological differences represent adaptations to their habitats, we tested for differences in both absolute and relative bite performance. Only absolute differences were found between forms, with the closed-canopy forms biting harder than their open-canopy counterparts. In contrast, sexual dimorphism was found for both absolute and relative bite force, but the relative differences were limited to the closed-canopy forms. These results indicate that both natural and sexual selection are acting within both habitat types, but to varying degrees. Sexual selection seems to be the predominant force within the closed-canopy habitats, which are more protected from aerial predators, enabling chameleons to invest more in ornamentation for communication. In contrast, natural selection is likely to be the predominant force in the open-canopy habitats, inhibiting the development of conspicuous secondary sexual characteristics and, ultimately, enforcing their overall diminutive body size and constraining performance.

Isolation of novel microsatellite loci in dwarf chameleons from KwaZulu-Natal province, South Africa and their cross-amplification in other Bradypodion species

A recently radiated clade of dwarf chameleon (genus Bradypodion) localised to central-southern KwaZulu-Natal province, South Africa is considered taxonomically problematic due to the observed discordance between morphology and genetics within and between its species. The clade is made up of two described species (B. melanocephalum–B. thamnobates) and possibly others—all of which are experiencing significant reductions in the quality and quantity of available habitat due to natural and anthropogenic factors. To better understand the effects past and present habitat fragmentation has had on gene flow, population structure, and genetic diversity within this clade, we developed seven new microsatellite markers for the B. melanocephalum–B. thamnobates complex, plus two markers for B. pumilum using an enrichment protocol. We tested these nine markers, along with eight markers previously designed for B. pumilum, for cross-species transferability across five species within the genus Bradypodion (B. melanocephalum, B. thamnobates, B. dracomonatum, B. sp. and B. pumilum). The number of alleles ranged from 1 to 29 with observed heterozygosities ranging from 0.00 to 1.00. Several loci did not meet HW expectations, but this may be a result of extreme demographic fluctuations that have been noted for these species. Ten loci were found to be polymorphic across all species examined, making them ideal for studies examining the population genetics of dwarf chameleons.

Does diet drive the evolution of head shape and bite force in chameleons of the genus Bradypodion

Summary 1.The head is a complex integrated system that is implicated in many vital functions. As such its morphology is impacted by different and sometimes conflicting demands. Consequently, head shape varies greatly depending on the environment and dietary ecology of an organism. Moreover, given its role in territory defence and mating in lizards, it is also subjected to strong sexual selection in these animals. 2.We investigated the relationships between head shape, bite performance, and diet in 14 of the 17 extant Bradypodion species to determine whether variation in diet can explain the observed diversity in bite force and head shape in this genus. We also evaluate differences between sexes in terms of the relationships between head shape, bite force, and diet and predict tighter relationships in females given that the head in this sex is principally under natural selection. 3.Our results show that there is indeed a correlation between head shape, diet, and bite force, but the direction and magnitude are sex dependent. Whereas we observed a correlation between absolute bite force and head shape in both sexes, size-corrected bite force was correlated with mandible and quadrate shape in females only. Despite strong correlations between bite force and prey hardness, and between prey hardness and head shape, we did not find any relationship between head shape and prey evasiveness. 4.These data suggest that the cranial system in chameleons of the genus Bradypodion evolves under natural selection for the ability to eat large or hard prey. Moreover, significant differences in the ecomorphological relationships between the two sexes suggest that sexual selection plays a role in driving the evolution of bite force and head shape. These data suggest that ecomorphological relationships may be sex-dependent. This article is protected by copyright. All rights reserved.

Analysis of genetic diversity in Rose’s mountain toadlet (Capensibufo rosei) using novel microsatellite markers

Abstract On the Cape Peninsula, Capensibufo rosei is known from only two isolated breeding populations within Table Mountain National Park. Because of its declining state, there is an urgent need to understand the genetic diversity, population structure and patterns of movement of this species. To do this, 15 microsatellite primer pairs were designed, optimised and tested. Successful loci were screened for null alleles and genotyping errors and then analysed, specifically noting the number of alleles, allelic size range, observed and expected heterozygosities, deviations from Hardy–Weinberg equilibrium (HWE) and linkage disequilibria. Bottleneck tests and analyses of molecular variance (AMOVA) were also conducted to gain insight into each population’s structure. Eleven primer pairs produced unambiguous polymerase chain reactions (PCR) products and scoreable bands, which were found to be polymorphic across both breeding populations. Deviations from HWE were detected owing to the presence of null alleles and inbreeding. Significant bottleneck signatures were detected for both populations and the AMOVA revealed significant differentiation between the two populations, indicating genetic structure at the population level.

Genetic diversity and differentiation of the Western Leopard Toad (Sclerophrys pantherina) based on mitochondrial and microsatellite markers

Abstract Intraspecific genetic diversity provides the basis for evolutionary change and is therefore considered the most fundamental level of biodiversity. Mitochondrial DNA (mtDNA) and microsatellite loci are the markers most typically used in population-level studies; however, their patterns of genetic variation are not always congruent. This can result in different interpretations of the data, which can impact on management decisions, especially for threatened species. Consequently, in this study, we developed and analysed novel microsatellite markers for the Endangered Western Leopard Toad (WLT), Sclerophrys pantherina, and compared the results to previously published mtDNA data to compare the level of genetic diversity between the two molecular markers. The microsatellite evidence showed signs of a past bottleneck, yet relatively high levels of genetic diversity and low genetic differentiation between two sampling sites. In contrast, the mtDNA revealed moderate to low levels of diversity between sampling sites, and strong genetic differentiation. An explanation for the conflicting patterns may be that the current genetic signature, as depicted by the microsatellite data, is not yet reflected in the mitochondrial dataset; and, as such the data are depicting a timeline for genetic variation within the WLT. Both markers revealed important information about the two sampling sites, which can help inform conservation management of the species.

Conservation genetics of an endemic and threatened amphibian (Capensibufo rosei): a leap towards establishing a genetic monitoring framework

Given the ever-increasing anthropogenic changes to natural ecosystems, it is imperative that temporal changes in genetic diversity be monitored to help safeguard the future viability of species. Capensibufo rosei is a small, range-restricted bufonid from South Africa, believed to have experienced an enigmatic decline likely due to the suppression of natural fires and the loss of grazing animals from some areas. Without these disturbances, their habitat becomes overgrown, which might affect the characteristics of their breeding pools. Since the 1980s, four breeding sites have been lost, presumably due to loss of breeding habitat through encroachment of vegetation. Currently, there are only two known populations [Cape of Good Hope (CGH) and Silvermine nature reserves] both within Table Mountain National Park. Consequently, this species may be vulnerable to stochastic events and genetic erosion through the loss of metapopulation connectivity. To assess the genetic status of this species, genetic diversity within both populations was quantified for two time periods using 11 microsatellite markers. Despite evidence of severe population bottlenecks, both populations possess levels of diversity similar to other anurans, and Silvermine has greater diversity than CGH. A close examination of the data revealed both populations to be genetically dynamic through time, with the loss and gain of rare alleles. Both populations also experienced a slight increase in overall diversity between sampling periods. While the latter was not statistically significant, the monitoring period was perhaps too short to understand changes in diversity over time. These results will form the baseline for future monitoring to better understand this threatened and declining species and to track genetic erosion or recovery.