Meeting Abstract

P1-105   -   Dissociation and natural selection on regions of the vertebral column in viperids Mollack, MG*; Hampton, PM; Colorado Mesa University; Colorado Mesa University pahampton@coloradomesa.edu

Snakes are often considered to have a relatively simple bauplan because they lack appendages. Nevertheless, among vertebrates snakes exhibit extraordinary variation in the number of vertebrae both within and among species. The numbers of pre-cloacal and caudal vertebrae have been identified as separate modules and under strong selection. Yet, investigation into the dissociation of modules within the pre-cloacal vertebral column and the ecological factors driving diversification in those regions has received relatively little consideration. We tested for dissociation in the number of vertebrae between the pre-cloacal region and tail and between the pre-atrial and post-atrial vertebrae in vipers. We then evaluated evolutionary changes between terrestrial and arboreal vipers using the number of vertebrae and relative body length for the pre-atrial, post-atrial and caudal portions of the vertebral column. We found that dissociation can occur between the number of pre- and post-atrial vertebrae though it was less likely than association. The number of caudal vertebrae exhibited the greatest interspecific variation indicating the tail is the most evolutionarily pliable of the three regions. Neither the pre- nor post-atrial (heart to cloaca) regions differed between habitat types for number of vertebrae, although terrestrial species attain greater pre-cloacal lengths as a result of larger body segments. Alternatively, arboreal species had longer relative tail lengths due to a greater number of caudal vertebrae. These results suggest that selection is working on body length proportions by adjusting both the abundance and size of vertebrae in vipers. Furthermore, these data provide evidence that interspecific variation in heart position in vipers is the result of the disproportionate addition or removal of vertebrae in regions of the vertebral column.