Browsing by Author "Tolley, Krystal A."

Now showing 1 - 7 of 7
  • Thumbnail Image
    Item
    Calibrating the tree of vipers under the fossilized birth-death model
    (Nature Research (part of Springer Nature), 2019-04-02) Smid, Jiri; Tolley, Krystal A.
    Scaling evolutionary trees to time is essential for understanding the origins of clades. Recently developed methods allow including the entire fossil record known for the group of interest and eliminated the need for specifying prior distributions for node ages. Here we apply the fossilized birth-death (FBD) approach to reconstruct the diversification timeline of the viperines (subfamily Viperinae). Viperinae are an Old World snake subfamily comprising 102 species from 13 genera. The fossil record of vipers is fairly rich and well assignable to clades due to the unique vertebral and fang morphology. We use an unprecedented sampling of 83 modern species and 13 genetic markers in combination with 197 fossils representing 28 extinct taxa to reconstruct a time-calibrated phylogeny of the Viperinae. Our results suggest a late Eocene-early Oligocene origin with several diversification events following soon after the group’s establishment. The age estimates inferred with the FBD model correspond to those from previous studies that were based on node dating but FBD provides notably narrower credible intervals around the node ages. Viperines comprise two African and an Eurasian clade, but the ancestral origin of the subfamily is ambiguous. The most parsimonious scenarios require two transoceanic dispersals over the Tethys Sea during the Oligocene.
  • Thumbnail Image
    Item
    Convergent evolution associated with habitat decouples phenotype from phylogeny in a clade of lizards
    (Public Library of Science, 2012-12-12) Edwards, Shelley; Vanhooydonck, Bieke; Herrel, Anthony; Measey, G. John; Tolley, Krystal A.
    Convergent evolution can explain similarity in morphology between species, due to selection on a fitness-enhancing phenotype in response to local environmental conditions. As selective pressures on body morphology may be strong, these have confounded our understanding of the evolutionary relationships between species. Within the speciose African radiation of lacertid lizards (Eremiadini), some species occupy a narrow habitat range (e.g. open habitat, cluttered habitat, strictly rupicolous, or strictly psammophilic), which may exert strong selective pressures on lizard body morphology. Here we show that the overall body plan is unrelated to shared ancestry in the African radiation of Eremiadini, but is instead coupled to habitat use. Comprehensive Bayesian and likelihood phylogenies using multiple representatives from all genera (2 nuclear, 2 mitochondrial markers) show that morphologically convergent species thought to represent sister taxa within the same genus are distantly related evolutionary lineages (Ichnotropis squamulosa and Ichnotropis spp.; Australolacerta rupicola and A. australis). Hierarchical clustering and multivariate analysis of morphological characters suggest that body, and head, width and height (stockiness), all of which are ecologically relevant with respect to movement through habitat, are similar between the genetically distant species. Our data show that convergence in morphology, due to adaptation to similar environments, has confounded the assignment of species leading to misidentification of the taxonomic position of I. squamulosa and the Australolacerta species.
  • Thumbnail Image
    Item
    Exploration into the hidden world of Mozambique's sky island forests : new discoveries of reptiles and amphibians
    (Pensoft, 2016) Conradie, Werner; Bittencourt-Silva, Gabriela B.; Engelbrecht, Hanlie M.; Loader, Simon P.; Menegon, Michele; Nanvonamuquitxo, Cristovao; Scott, Michael; Tolley, Krystal A.
    We carried out a survey of reptiles and amphibians within Afromontane forest and woodland slopes of three inselbergs in northern Mozambique (Mount Mabu, Mount Namuli, and Mount Ribáuè). A total of 56 species (22 amphibians and 34 reptiles) were recorded during the current survey. Our findings substantially increase the number of herpetofaunal species recorded from these mountains (Mount Ribáuè 59%, Mount Mabu 37%, and Mount Namuli 11% of the total species), including one new country record and several putative new species. An updated checklist of the herpetofauna of these mountains is presented.
  • Thumbnail Image
    Item
    Mind the gaps : investigating the cause of the current range disjunction in the Cape Platanna, Xenopus gilli (Anura: Pipidae)
    (PeerJ, 2013) Fogell, Deborah J.; Tolley, Krystal A.; Measey, G. John
    Low-lying areas of the Cape at Africa’s south-westernmost tip have undergone dramatic marine-remodelling, with regular changes in sea-level following glacial cycles. Species for which marine barriers are impenetrable underwent concomitant radical distribution changes which may account for current range disjunctions. The Cape platanna, Xenopus gilli, is a frog distributed in only three disjunt areas within low-lying regions of the southwestern Cape. We determined the relationship between frogs from these three disjunct areas, by using a combination of morphometric analysis and mtDNA (ND2 and 16S fragments) sequences of 130 frogs from eight ponds. Coalescent analyses on molecular data dated the divergence in two major clades to around 4.6 Mya, a period during which major uplifting on the eastern side of the subcontinent caused climate changes throughout southern Africa. Principal components analysis showed significant morphometric differences between each clade on head and limb measurements. Consistent differences in ventral colouration and patterning were also observed. We report on increased levels of hybridisation with X. laevis throughout the range of X. gilli, which reaches at least 27% hybrids in some ponds. Urgent conservation actions are required to control habitat loss from alien invasive vegetation, and prevent introgression with the domestic-exotic, X. laevis.
  • Thumbnail Image
    Item
    Sequential fragmentation of Pleistocene forests in an East Africa biodiversity hotspot : chameleons as a model to track forest history
    (Public Library of Science, 2011-10-28) Measey, G. John; Tolley, Krystal A.
    Background The Eastern Arc Mountains (EAM) is an example of naturally fragmented tropical forests, which contain one of the highest known concentrations of endemic plants and vertebrates. Numerous paleo-climatic studies have not provided direct evidence for ancient presence of Pleistocene forests, particularly in the regions in which savannah presently occurs. Knowledge of the last period when forests connected EAM would provide a sound basis for hypothesis testing of vicariance and dispersal models of speciation. Dated phylogenies have revealed complex patterns throughout EAM, so we investigated divergence times of forest fauna on four montane isolates in close proximity to determine whether forest break-up was most likely to have been simultaneous or sequential, using population genetics of a forest restricted arboreal chameleon, Kinyongia boehmei. Methodology/Principal Findings We used mitochondrial and nuclear genetic sequence data and mutation rates from a fossil-calibrated phylogeny to estimate divergence times between montane isolates using a coalescent approach. We found that chameleons on all mountains are most likely to have diverged sequentially within the Pleistocene from 0.93–0.59 Ma (95% HPD 0.22–1.84 Ma). In addition, post-hoc tests on chameleons on the largest montane isolate suggest a population expansion ∼182 Ka. Conclusions/Significance Sequential divergence is most likely to have occurred after the last of three wet periods within the arid Plio-Pleistocene era, but was not correlated with inter-montane distance. We speculate that forest connection persisted due to riparian corridors regardless of proximity, highlighting their importance in the region's historic dispersal events. The population expansion coincides with nearby volcanic activity, which may also explain the relative paucity of the Taita's endemic fauna. Our study shows that forest chameleons are an apposite group to track forest fragmentation, with the inference that forest extended between some EAM during the Pleistocene 1.1–0.9 Ma.
  • Thumbnail Image
    Item
    Sexual dimorphism in bite performance drives morphological variation in chameleons
    (PLoS, 2014-01-27) Da Silva, Jessica M.; Herrel, Anthony; Measey, G. John; Tolley, Krystal A.
    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.
  • Thumbnail Image
    Item
    Survival and abundance of Cape dwarf chameleons, Bradypodion pumilum, inhabiting a transformed, semi-urban wetland
    (British Herpetological Society, 2013) Katz, Eric M.; Tolley, Krystal A.; Altwegg, Res
    The Cape dwarf chameleon, Bradypodion pumilum, inhabits urban areas within a critically endangered ecosystem. In this study, temporal dynamics of local demographic parameters were investigated for a population of B. pumilum inhabiting a 0.56 hectare patch of transformed habitat bordering an urban area in Noordhoek, South Africa. Robust Design (RD) capture-mark-recapture (CMR) models were used to estimate population demographics because of their ability to distinguish and account for temporary unavailability of individuals versus being captured. RD models were fit to one year of CMR data to examine adult survival and local abundance. Additionally, multi-strata (MS) models were used to analyze chameleon growth rate and size-specific survival. The results indicate the site supports a fluctuating abundance of individuals, ranging from ca. 25–91 adult chameleons. Larger chameleons showed higher 30-day and annual survival rates than smaller individuals regardless of sex (30-day range: 0.56–0.84; annual range: 9.51x10-5–0.12). Chameleons that survived to the beginning of each age class spent on average 1.1 months at 40–50 mm; 1.7 months at 50–60 mm; 2.5 months at 60–70 mm; and 6.3 months at >70 mm. Despite seasonality in the environment, there was no significant seasonal variation in chameleon survival. These findings indicate chameleon population dynamics characterized by local population fluctuations despite predominately constant, low survival; our findings suggest reproduction drives population fluctuations. Bradypodion pumilum's high fecundity and low survival should allow for their persistence in disturbed habitats assuming they are able to take advantage of suitable conditions. Alternatively, these biological traits may make B. pumilum prone to large demographic fluctuations, yielding a high risk of local extinction. This study provides temporal data on local population dynamics and survival for a potentially threatened reptile species inhabiting altered habitats.