A central question in modern biology is the evolution of morphological diversity. How does form in one species, where it presumably fits the creature to life in its habitat, change to a different form in descendant species, where each again must be fitted to life in its environment? One approach used to address this problem is to determine how changes in the morphological development of embryos have contributed to evolutionary changes in the form or structure of adult organisms. This developmental approach increasingly is being emphasized by morphologists, in conjunction with molecular data that provide a phylogenetic framework for the group of organisms under study. The skulls of snakes are highly complex in comparison with most other vertebrates; their structure is closely related to such functions as feeding and in supporting and protecting the brain and sense organs; but changes in skull morphology among snake species are not well understood, either developmentally or evolutionarily. Faculty advisers Virginia Roth and Alan Savitsky will direct graduate student William Velhagen in a study of the pattern and timing of development of the cranial bones of thamnophiine snakes, the group that includes the gartersnakes and watersnakes. Although closely related genealogically, the thamnophiines are diverse in their morphology and habits: some are large and eat fish and amphibians; some are small and feed only on soft-bodied invertebrates like earthworms; still others feed exclusively on crayfish. In analyzing the embryonic development of the thamnophiine skull within the context of the evolutionary history of the group (derived from independent molecular data) and the known feeding adaptations of the species, insight will be gained about the direction and extent of developmental change in closely related species. The study will contribute to the general issue of whether, and to what degree, particular embryonic developmental events constrain or facilitate change in adult form.
