An investigation of the evolutionary diversification of a recent radiation of dwarf chameleons (Bradypodion) from KwaZulu-Natal Province, South Africa

Da Silva, Jessica Marie (2014-04)

Thesis (PhD)--Stellenbosch University, 2014.

Thesis

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.

AFRIKAANSE OPSOMMING: 'n Belangrike voorvereiste vir evolusionêre verandering is variasie in natuurlike bevolkings, maar wanneer fenotipiese en molekulêre tempo van verandering verskil, is spesies definieering problematies. Sulke onenigheid is geïdentifiseer in ‘n onlangse radiasie van dwerg verkleurmannetjies (Bradypodion) van die KwaZulu-Natal Provinsie, Suid-Afrika. Hierdie radiasie bestaan uit verskeie fenotipiese vorms, waarvan twee taksonomies geklassifiseer is – Bradypodion melanocephalum en Bradypodion thamnobates. Vroeë filogenetiese analise het nie die vorms ondersteun nie, hoofsaaklik omdat geografiese steekproefneming en die stel van molekulêre merkers gebruik geskik was vir die opsporing van diep afwykings, en dus minder effektief is vir die begrip van spesies grense binne 'n onlangse radiasie. In hierdie radiasie is die vorms allopatries, beset verskillende habitatte, en wissel in grootte en kleur, wat dui op plaaslike aanpassing en ekologiese spesiasie. Om hierdie hipotese te toets, is morfometriese en habitat gegewens ingesamel vir elke vorm om sodoende ekologies relevante morfologiese verskille te ondersoek wat verskil in habitat gebruik reflekteer. Morfologiese verskille is geassosieer met funksionele aanpassings deur lokomotoriese prestasie en byt krag te toets. Volgende is fyn-skaal genetiese steekproefneming gebruik om afkoms diversifikasie met behulp van 'n kombinasie van mitochondriale DNS en mikrosatelliete ondersoek. Ruimtelike inligting is geinkorporeer in die ontleding om sodoende genetiese gevolge van landskap hindernisse op genetiese struktuur te kwantifiseer. Ten slotte, is ekologiese nis modelle gebruik om die abiotiese faktore wat betrokke is by die vorming van klimaat- nisse van hierdie verkleurmannetjie te ondersoek en om insig te verkry oor hul biografiese geskiedenis. Resultate toon morfologiese onderskeid tussen fenotipiese vorms, met saameenlopende verskille in prestasie, wat dui op funksionele aanpassings tot habitat, wat breedweg as oop- of geslote-kap plantegroei geklassifiseer kan word. Spesifiek verkleurmannetjies in oopkap habitatte het proporsioneel kleiner koppe en voete as hul geslote-kap eweknieë, en ooreenkomstig swakker byt krag en voorvoet greep. Wisselende vlakke van seksuele dimorfisme is vasgestel, met geslote-kap vorms wat meer dimorfies is as oop-kap vorms. Dit dui daarop dat seksuele seleksie die oorheersende krag in geslote-kap habitatte is, wat meer beskerm is teen vlieënde roofdiere, wat hulle in staat stel om te belê in dimorfiese eienskappe vir kommunikasie, terwyl in oop-kap habitatte, is natuurlike seleksie die oorheersende krag, wat uiteindelik kleiner liggaam grootte en beperkte prestasie afdwing. Genetiese struktuur is waargeneem, met die onthulling van drie genetiese groeperings gebasseer op mitochondriale DNS en sewe gebasseer op mikrosatelliete. Dit weerspieël waarskynlik die verskil in mutasie tempo en manier van erfenis tussen hierdie twee merkers. Drie van die mikrosatelliet groeperings is ondersteun deur morfologiese en ekologiese gegewens en moet dus erken word as aparte spesies. Die oorblywende mikrosatelliet groeperings dui op onenigheid met eko-morfologiese data, maar, gegewe hul genetiese eiesoortigheid, moet hulle erken word as afsonderlike bewarings eenhede. Die klimaat-nisse van die drie voorgestelde spesies het hoë tot matige vlakke van die klimaat stabiliteit, terwyl die vier voorgestelde bewarings eenhede lae klimaat stabiliteit het. Hierdie resultate dui daarop dat hierdie spesie kompleks beïnvloed word deur beide klimaat nis konserwatisme en stabiliteit, wat die waargenome patrone van morfologiese en genetiese diversiteit kan verduidelik. In opsomming, hierdie resultate ondersteun die hipotese van ekologiese spesiasie binne hierdie radiasie.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/86306
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