Ecomorphological forms in Dwarf Chameleons (Bradypodion): assessment of functional morphology and gene flow across spatially adjacent habitat types

Potgieter, Daniel Francois (2013-03)

Thesis (MSc)--Stellenbosch University, 2013.

Thesis

ENGLISH ABSTRACT: Adaptive radiation is the process whereby clades, lineages, or species demonstrate rapid divergence into an array of phenotypic forms. Variation in ecological parameters, such as habitat use and morphology or behavioural traits related to communication; drive the evolution of ecologically relevant traits in specific habitat types. Nevertheless, such processes may be countered or enhanced by sexual selection pressures as selection acts on the phenotype to maximise reproductive output. Within the Cape Floristic region, species of dwarf chameleons (Bradypodion) are showing signs of such an adaptive radiation. Previous work on B. pumilum revealed intraspecific morphological differentiation, emphasised by functional differences in ecologically relevant traits, between those occupying the fynbos and forest/riverine thicket habitat types. Similar phenotypic divergences are hypothesised to have occurred in their allopatric, forest-dwelling neighbour, the Knysna Dwarf Chameleon (B. damaranum), given the presence of a closely related, morphologically divergent, undescribed species (B. sp. 1) found in the adjacent fynbos habitat type. With this in mind, functional morphological variation was examined between these two potential ecomorphological forms. A second unidentified fynbos species (B. sp. 2), which neighbours these species in its distribution, served to substantiate the proposed morphology~performance~habitat hypotheses. Given the chameleon’s strong reliance of vegetation type, habitat use was explored by examining the microhabitat relevant to chameleons and ascertaining whether this habitat is used randomly. To associate variation in morphology with differences in habitat use, differences in performance capabilities were quantified, particularly those associated with grip strength (hand and tail) and sprint speed. Furthermore, twelve microsatellite markers were used in combination with the ND4 mitochondrial marker to understand the fine scale patterns of gene flow both within and between habitat types. In response to the varied pressures experienced, differences in ecologically relevant traits are found between B. damaranum and the two fynbos species, particularly those related to locomotion (limb length) and bite force (head width). Furthermore, analysis of microhabitat features shows that the fynbos and forest habitat types are structurally different, facilitating differences in habitat use. Differences in performance also vary between vegetation types, with B. damaranum possessing stronger hand and tail grip forces as well as faster sprint speeds. Sexual dimorphism is also present; however it is more prominent in the forest-dwelling B. damaranum. Genetic analyses revealed high levels of geographical structure between B. sp. 1 and B. damaranum, suggesting the presence of a strong barrier to gene flow. Given the congruence between morphological divergence and genetic spatial patterns, it appears that this barrier is associated with habitat type. Within each habitat type, both mtDNA and microsatellite analyses reveal congruent patterns of structuring. These patterns are, however, not governed by barriers to gene flow, but rather via isolation by distance (based on microsatellite data). Furthermore, mtDNA analysis confirmed B. sp. 2 to be highly divergent, occupying a separate clade to B. sp. 1 and B. damaranum. The adaptive differences observed between B. damaranum and B. sp. 1, coupled with its overall resemblance to those observed in B. pumilum; suggest the presence of true chameleon ecomorphs in the genus Bradypodion. This coupled with the lack of gene flow between ecomorphs is indicative of a true allopatric diversification.

AFRIKAANSE OPSOMMING: Adaptiewe radiasie is die proses waardeur genetiese groepe, lyne, of spesies vinnige divergeer na ‘n verskeidenheid van fenotipiese vorms. Variasie in ekologiese parameters, soos habitat verbruik en morfologie of gedrags eienskappe met betrekking tot kommunikasie, dryf die evolusie van ekologies relevante eienskappe in spesifieke habitat tipes. Nieteenstande, kan sulke prosesse teengewerk of versterk word deur seksuele seleksie omdat hierdie seleksie optree om die spesifieke fenotipe se reproduktiewe uitset te maksimaliseer. In die Kaapse Floristiese streek, toon spesies van die dwerg verkleurmannetjie (Bradypodion) tekens van 'n adaptiewe radiasie. Vorige werk op B. pumilum het intraspesifieke morfologiese differensiasie aan die lug gebring, beklemtoon deur funksionele verskille in ekologies relevante eienskappe, tussen diere wat uitsluitlik binne die fynbos of die woud/oewer tiepe habitat woon. Daar word gespekuleer dat soortgelyke fenotipiese verskille plaasgevind het binne hul allopatriese, woudlewende familie-lid, die Knysna dwergverkleurmannetjie (B. damaranum), gegewe die teenwoordigheid van 'n nou verwante, morfologies uiteenlopende, onbeskryfde spesies (B. sp. 1) wat in die aangrensende fynbos habitat aangetref word. Met dit in gedagte is funksionele morfologiese variasie tussen hierdie twee potensiële ekomorfologiese vorms ondersoek. ‘n Tweede onbekende fynbos spesies (B. sp. 2), waarva dje versreiding langsliggend is aan hierdie speisies, is gebruik om die voorgestelde morfologie ~ prestasie ~ habitat hipoteses te staaf. Omdat die verkleurmannetjie afhanklikheid is van plantegroei tipe, het hierdie studie habitat gebruik ondersoek deur die mikrohabitat te bestudeer wat deur willekeurig hierdie diere gebruik word. Om die variasie in morfologie met verskille in habitat gebruik om te assosieer, is verskille in prestasie vermoëns gekwantifiseer, veral dié wat verband hou met greep krag (hand en stert) en hardloop spoed. Verder is twaalf mikrosatelliet merkers gebruik in kombinasie met die ND4 mitochondriale merker om fyn-skaal patrone van gene-vloei te verstaan beide binne en tussen habitat tipes. In reaksie op die uiteenlopende evolusionêre drukke is verskille in ekologies relevante eienskappe gevind tussen B. damaranum en die twee fynbos spesies, veral dié met betrekking tot voortbeweging (ledemaat lengte) en byt krag (kop breedte). Verder, het die analise van mikrohabitat kenmerke getoon dat die fynbos en woud habitat tipes struktureel verskil, en dit fasiliteer dus die verskille in habitat gebruik. Verskille in prestasie het ook gewissel ook tussen plantegroeitipes deurdat B. damaranum 'n sterker hand en stert greep sowel as vinniger hardloop spoed getoon het. Seksuele dimorfisme is ook teenwoordig, maar dit is meer prominent in die woud-bewoning B. damaranum. Genetiese analyses het hoë vlakke van geografiese struktuur tussen B. sp. 1 en B. damaranum aan die lig gebring, wat dui op die teenwoordigheid van 'n formidabile grens tot genevloei. Gegewe die ooreenkomste tussen morfologiese divergensie en genetiese ruimtelike patrone, blyk dit dat hierdie grens tot genevloei verband hou met die habitat tipe. Binne elke tipe habitat, het buide mtDNA en mikrosatelliet analises dieselfde geneties patrone. Hierdie genetiese patrone word nie gereeld deur grense tot geenvloei beïnvloed nie, maar eerder deur isolasie met afstand (gebaseer is op die mikrosatelliet data). Verder, mtDNA analises bevestig dat B. sp. 2 verreweg geneties verwant is en ‘n afsonderlike klade vorm het relative tot die B. sp. 1 en B. damaranum. Die aanpasbare verskille wat waargeneem tussen B. damaranum en B. sp. 1, tesame met die ooreenkomste aan dié waargeneem met B. pumilum; dui op die teenwoordigheid van ware verkleurmannetjie ekomorfs in die genus Bradypodion. Dit, tesame met die gebrek van genevloei tussen ekomorfs, is 'n aanduiding van 'n ware allopatriese diversifikasie.

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