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Title: Geometric morphometric analysis of the breast-shoulder apparatus of Greater Antillean anole ecomorphs
Author: Tinius, Alexander
Advisor: Russell, Anthony
Keywords: Zoology
Issue Date: 27-Jan-2016
Abstract: Anoline lizards of the Greater Antillean islands have repeatedly followed parallel paths of morphological adaptation, resulting in ecologically and morphologically similar ecomorph communities (ecomorphs) on each island. Locomotor performance has been shown to be a key factor related to differential microhabitat occupancy of anoles, but to date studies on possible differences in the form and configuration of the postcranial skeleton and musculature (deep anatomy) that relate to ecomorphological differentiation are scant. Here I employ the breast-shoulder apparatus (BSA; the skeleton, musculature, and connective tissue that comprise the pectoral region of tetrapods) to examine the morphological variability of the pectoral region of island anoles. I employ microcomputed tomography to image the skeletal elements of the BSA, and three-dimensional geometric morphometric analysis to compare the shapes of the skeletal features of twenty-six anole species representing four distinctive ecomorphs (trunk-ground, trunk-crown, crown-giant, twig). My material is sourced from three Greater Antillean islands (Jamaica, Puerto Rico, and Hispaniola). Despite several limitations of the techniques employed, I show that a comprehensive understanding of the interactions between ecological preferences and morphological adaptations can only be gained from an investigation of the complex integration of form, function, and ecological role. The geometry of the shoulder girdle in situ, and that of its components, differs between anole species. These morphological differences show a hierarchy of influences: they are primarily driven by ecomorph designation, but are also influenced by patterns of phylogenetic relationship, which contrasts with the findings from linear measurements and counts used to characterise ecomorphs. The three arboreal ecomorphs are characterised by a differential shape of the presternum, which is likely associated with changes in the musculature of these anoles, and made possible through the insensible transition between the pre- and mesosternum, facilitating migration of the rib attachment sites. This has potentially facilitated adaptive radiation in anoles. My investigations further show that linear external measurements cannot be employed to predict patterns of variation in the skeletal elements of the BSA. Varying environmental factors on the three islands examined allowed for the occurrence of similar, but not identical, skeletal patterns of ecological-morphological adaptation in geographically distinct areas.
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