Doctoral Degrees (Conservation Ecology and Entomology)

Permanent URI for this collection

https://scholar.sun.ac.za/handle/10019.1/531

Browse

Browsing Doctoral Degrees (Conservation Ecology and Entomology) by Author "Da Silva, Jessica Marie"

Now showing 1 - 1 of 1
  • Thumbnail Image
    Item
    An investigation of the evolutionary diversification of a recent radiation of dwarf chameleons (Bradypodion) from KwaZulu-Natal Province, South Africa
    (Stellenbosch : Stellenbosch University, 2014-04) Da Silva, Jessica Marie; Tolley, Krystal A.; Knight, Andrew T.; Stellenbosch University. Faculty of AgriSciences. Dept. of Conservation Ecology and Entomology.
    ENGLISH ABSTRACT: An important prerequisite for evolutionary change is variability in natural populations; however, when phenotypic and molecular rates of change differ, species delimitation is problematic. Such discordance has been identified in a recent radiation of dwarf chameleons (Bradypodion) from KwaZulu-Natal Province, South Africa. This radiation is comprised of several phenotypic forms, two of which have been classified taxonomically – Bradypodion melanocephalum and Bradypodion thamnobates. Early phylogenetic analysis did not support the forms primarily because geographic sampling and the set of molecular markers used were appropriate for detecting deep divergences and, therefore, less effective for understanding species boundaries within a recent radiation. In this radiation, the forms are allopatric, occupy different habitats, and vary in size and colouration, suggesting local adaptation and ecological speciation. To test this hypothesis, morphometric and habitat data were collected for each form to examine ecologically relevant morphological differences that reflect differential habitat use. Morphological differences were then associated with functional adaptations by testing locomotor performance and bite force. Next, fine-scale genetic sampling was used to examine lineage diversification using a combination of mitochondrial DNA and microsatellites. Spatial information was incorporated into these analyses to quantify the genetic effects of landscape barriers on genetic structure. Finally, ecological niche modelling was used to examine the abiotic factors involved in shaping the climatic niches of these chameleons, and to gain insight into their biogeographic history. Results show morphological distinctions between phenotypic forms, with corresponding differences in performance, indicating functional adaptations to habitats, which can be broadly classified as either open- or closed-canopy vegetation. Specifically, chameleons in open-canopy habitats have proportionally smaller forces and forefoot grip strengths. Varying degrees of sexual dimorphism were detected, with the closed-canopy forms being more dimorphic than the open-canopy forms. This suggests that sexual selection is the predominant force within the closed-canopy habitat, which are more protected from aerial predators, thereby enabling them to invest in dimorphic traits for communication; while, in open-canopy habitats, natural selection is the predominant force, ultimately enforcing their overall diminutive body size and constraining performance. Genetic structure was observed, with the mitochondrial DNA revealing three genetic clusters and the microsatellites revealing seven. This likely reflects the different mutation rates and modes of inheritance between these two markers. Three of the microsatellite clusters were supported by morphological and ecological data and should, therefore, be recognised as separate species. The remaining microsatellite clusters showed discordance with the ecomorphological data; however, given their genetic distinctiveness, they should be recognized as separate conservation units. The climatic niches of the three proposed species showed high to moderate levels of climatic stability, while the four proposed conservation units showed low climatic stability. These results indicate that this species complex is affected by both climatic niche conservatism and lability, which could explain the observed patterns of morphological and genetic diversity. In summary, these results support the hypothesis of ecological speciation within this radiation.