Investigating the morphology, locomotory performance and macroecology of a sub-Saharan African frog radiation (Anura: Pyxicephalidae)

Rebelo, Alexander Douglas (2017-03)

Thesis (MSc)--Stellenbosch University, 2017.

Thesis

ENGLISH ABSTRACT: The phenotypic diversity among closely related species is often attributed to the process of natural selection. This process retains heritable traits within a population, increasing effectiveness of movement within the environment they occupy to maximise their fitness. Morphological traits can be selected to modify aspects of locomotion to better suit certain requirements. Such traits could also have an effect on distributional patterns, and could drive large-scale macroecological patterns. Understanding how interspecific differences in morphology relate to functional and distribution patterns can provide clues to the evolutionary and macroecological processes that drive them. In this study I compare interspecific differences in morphology and locomotor performance of the Pyxicephalidae. I hypothesise that morphology will affect locomotor performance and that these differences are best explained by the habitat and ecology of the species. Additionally I investigate whether morphological and reproductive traits can explain interspecific differences in geographic range size; and use modelling to determine their affect on colonisation ability and niche breadth. Morphology and locomotion was assessed for 25 wildcaught pyxicephalid species. Swimming and jumping performance was filmed at a high-frame rate, endurance was assessed by chasing frogs around a circular track and adhesive performance by rotating frogs on a non-stick surface. Specimens were measured and dissected from museums for reproductive and additional morphological data. Range size was calculated using a minimum convex polygon from distributional data. MaxEnt was used to model habitat suitability with Worldclim and topographic predictors. Colonisation Index was derived from habitat suitability to quantify the ability of a species to occupy nearby suitable habitats and niche breadth was calculated with the Outlier Mean Index (OMI) analysis, using the same predictor variables, but constraining the geographic extent to South Africa and species therein. Species morphology had a significant influence on the measured locomotive traits, which confirmed similar functional relationships found for other frog clades. Furthermore, I find support that separate selective optima for morphology between burrowing, terrestrial and semi-aquatic ecotypes, but not for locomotor performance. However, specific tests between traits showed that semi-aquatic ecotypes had support for a separate performance selective optimum. Species geographic range size was positively correlated with body size and relative clutch size, but not relative head width or hindlimb length. The Colonisation Index was not robust for comparing species from different environments and range extents. Species niche breadth was not explained by either body size or relative clutch size, but by relative hindlimb length, suggesting that these former traits do not affect range size by increasing species ability to colonise and occupy a broader range of environmental conditions. In summary, species body size and reproductive output are indirectly linked to range size patterns, but these patterns appear to be the result of an indirect association with abundant habitats or the ability to disperse and colonise within suitable habitat. The morphological diversity of the Pyxicephalidae has functional significance for locomotor performance, and some of these traits do represent ecotype adaptations. However, the limited evidence presented in this study does not support the Pyxicephalidae as an adaptive radiation.

AFRIKAANSE OPSOMMING: Die fenotipiese diversiteit tussen nouverwante spesies word dikwels toegeskryf aan die proses van natuurlike seleksie. Hierdie proses behou oorerflike eienskappe binne 'n doeltreffende beweging wat die oorlewing verhoog binne in hulle omgewing. Seleksie van morfologiese eienskappe kan lei tot aanpassings wat aspekte van beweging beïnvloed om hul behoeftes beter te pas. Hierdie eienskappe kan 'n uitwerking op verspreidingspatrone, en grootskaalse makro-ekologiese patrone te hê. Hoe die interspesifieke verskille in die morfologie verband hou met die funksionele en verspreidingspatrone, kan aandui hoe die evolusionere en makro-ekologiese prosesse die patrone beinvloed. In hierdie studie vergelyk ek interspesifieke verskille in morfologie en lokomotoriese prestasie van die Pyxicephalidae. My hipotese is dat morfologie die lokomotoriese prestasie sal beïnvloed en dat hierdie verskille verander met habitat en ekologie. Verder het ek kyk of die morfologiese en reproduktiewe kenmerke die grootte van die geografiese verskeidenheid kan verduidelik en gebruik modelleer die kolonisasie vermoë en nisbreedte. Morfologie en voortbeweging was vir 25 pyxicephalid spesies beoordeel. Swem en spring prestasie is getoets deur stadige aksie verfilming; uithouvermoë was bepaal deur die paddas te jaag om „n sirkelvormige baan; en adhesie is gemeet op 'n kleefvrye oppervlak wat gedraai was. Paddas van museums was gemeet en ontleed om morfologiese en reproduktiewe kenmerke te kry. Verspreidings grootte was bereken met behulp van 'n minimum konvekse veelhoek vir verspreiding data. MaxEnt is gebruik om habitat geskiktheid met Worldclim en topografiese voorspellers te modelleer. Kolonisasie indeks is afgelei van habitat geskiktheid om die vermoë van 'n spesie om nabygeleë geskikte habitate te gebruik te kwantifiseer. Breedte bereken met die ontleding Uitskieter Gemiddelde Indeks (OMI), met hulp van dieselfde voorspeller veranderlikes, maar met die beperking van die geografiese mate tot Suid-Afrikaanse en spesies daarin. Die morfologie van spesies het 'n beduidende invloed op lokomotoriese prestasie wat gemeet was. Verder vind ek ondersteunende bewyse dat verskillende selektiewe optima vir morfologie tussen grawende, land- en semi-akwatiese eko-tipes, maar nie vir lokomotoriese prestasie nie. Spesifieke toetse wat gedoen was tussen eienskappe wys dat semi-akwatiese paddas 'n verskillende selektiewe optimale vir lokomotoriese prestasie het in vergelyking met die ander eko-tipe hê. Die geografiese verskeidenheid in grootte van die paddas is positief gekorreleer met liggaamsgrootte en relatiewe broeiselgrootte, maar is nie gekorreleer met relatiewe kop breedte of agterbeen lengte nie. Die nisbreedte van spesies kan nie verduidelik word deur liggaamsgrootte of relatiewe broeiselgrootte nie, maar kan verduidelik word deur relatiewe agterbeenlengte, wat daarop dui dat hierdie voormalige eienskappe beinvloed nie die verskeidenheid grootte deur die verhoging van spesies vermoë om te koloniseer nie. Om op te som, spesies liggaamsgrootte en reproduktiewe uitset is indirek gekoppel aan die gebiedserspreidings patrone maar dit lyk asof hierdie patrone verduidelik kan word deur indirekte assosiasie tussen die beskikbaarheid van habitatte en die vermoë van 'n spesies om te versprei en te koloniseer in beskikbare habitatte. Die morfologiese diversiteit van die Pyxicephalidae het funksionele betekenis vir lokomotoriese prestasie, en 'n paar van hierdie eienskappe verteenwoordig eko-tipe-aanpassings. Die beperkte bewyse van hierdie studie ondersteun nie die Pyxicephalidae as 'n aanpasbare radius.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/101468
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