THE ROLE OF HABITAT SHIFT IN THE EVOLUTION OF LIZARD MORPHOLOGY - EVIDENCE FROM TROPICAL TROPIDURUS

We compared morphology of two geographically close populations of the tropical lizard Tropidurus hispidus to test the hypothesis that habita t structure influences the evolution of morphology and ecology at the population level. T. hispidus isolated on a rock outcrop surrounded by tropical forest use rock crevices for refuge and appear dorsoventrall y compressed compared with those in open savanna. A principal componen ts analysis revealed that the populations were differentially distribu ted along an axis representing primarily three components of shape: bo dy width, body height, and hind-leg length. Morphological divergence w as supported by a principal components analysis of size-free morpholog ical variables. Mitochondrial DNA sequences of ATPase 6 indicate that these populations are closely related relative to other T. hispidus, t he rock outcrop morphology and ecology are derived within T. hispidus, and morphological and ecological divergence has occurred more rapidly than genetic divergence. This suggests that natural selection can rap idly adjust morphology and ecology in response to a recent history of exposure to habitats differing in structure, a result heretofore impli ed from comparative studies among lizard species.