Browsing by Author "Rebelo, Alexander Douglas"

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    Investigating the morphology, locomotory performance and macroecology of a sub-Saharan African frog radiation (Anura: Pyxicephalidae)
    (Stellenbosch : Stellenbosch University, 2017-03) Rebelo, Alexander Douglas; Measey, John; Stellenbosch University. Faculty of Science. Dept. of Botany and Zoology.
    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.