VINCENT, S. E. ; IRSCHICK, D. J. ; HERREL, A. ; Tulane University: Has head shape evolved to match feeding mode in natricine snakes? Convergence and constraints

Macrostomatan snakes have independently evolved multiple feeding modes (e.g., piscivory, dietary generalist) and are often dietary specialists. Because snakes are gape-limited predators, it is generally thought that a strong link exists between a snake�s feeding mode and its overall head shape, but few studies have addressed this issue in an evolutionary context. Here we assess whether snakes that have independently evolved similar feeding modes have also evolved similar head shapes by examining 23 species of natricine snakes. Our ancestral reconstruction of feeding mode shows that specialization for piscivory and earthworm consumption, as well as dietary generalization have all independently evolved several times within this group. However, a frog and fish feeding mode (species that regularly consume only fish and amphibians) has evolved only once within the Nerodia species complex. Our phylogenetically corrected analysis of head shape revealed that most piscivores, frog and fish feeders, and earthworm specialists cluster closely with their respective centroids in morphological space. However, several piscivores clustered closely within the frog and fish feeding group, two of which were Nerodia species. By contrast, dietary generalists displayed a high degree of morphological variance. As a result, we suggest that within this group of Macrostomatan snakes, species that feed on similar prey types typically have comparable head shapes independent of phylogeny, with the exception of dietary generalist snakes.