Meeting Abstract

44.2  Thursday, Jan. 5  Evolution of Cranial Modularity in Caecilians SHERRATT, E*; WILKINSON, M; GOWER, DJ; KLINGENBERG, CP; Harvard University, Cambridge, MA; The Natural History Museum, London, UK; The Natural History Museum, London, UK; The University of Manchester, Manchester, UK

Morphological integration is a biological phenomenon describing the coordination among morphological subunits. The related concept of modularity is the degree of integration within and between these subunits, and can be inferred from patterns of covariation among measured traits. We used geometric morphometrics to investigate modularity in the cranium of 141 species of caecilians - limbless and mostly burrowing amphibians that use their head as a tool for locomotion. Taking a developmental and evolutionary perspective, we examined covariation at three levels of variation: within individuals (fluctuating asymmetry), within species and among species. We evaluated two a priori hypotheses of modularity that defined functionally distinct regions of the cranium as modules, and found support for one, where the cranium is modular with respect to the snout and the braincase with cheek region. The modularity hypothesis was supported at all levels, indicating there is a developmental basis for the modularity, which is shared among all species of caecilians. We examined patterns of evolutionary shape variation for each module and found that they substantially differ, where the snout has undergone greater morphological diversification during history of caecilians than the braincase with cheek region module. We interpret this pattern as support to the theory that modularity may facilitate adaptive evolution by allowing independent changes to underlying developmental interactions within a module without disrupting the function of the entire organism.