Molecular Phylogenetics and the Evolution of Rattlesnakes [Crotalus and Sistrurus]

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A grant has been awarded to Dr. Kelly R. Zamudio and Dr. Harry W. Greene at Cornell University to study rattlesnake evolution. The 28 species comprise a group of ecologically diverse New World pitvipers with unique tail shaker muscles and noise-making segments on their modified tail tips. Despite widespread interest by scientists and the public, previous inferences about their origin and diversification were made prior to recent innovations in molecular systematics. No evidence exists for a widespread belief that rattles evolved in response to bison herds, for example, and new statistical approaches for studying biogeography and character evolution have not previously been applied to this topic. Zamudio and Greene will sequence the DNA in several nuclear and mitochondrial genes of rattlesnakes and their relatives, with the immediate goals of reconstructing their relationships and biogeographic history, then testing five alternative scenarios of rattle origin. Rattlesnakes play increasingly prominent roles in anthropology, ecology, evolutionary biology, conservation, and biomedical research, topics on which Zamudio and Greene's findings will provide important comparative perspectives. Rattlesnakes are important predators and knowledge of evolutionary relationships will elucidate the roles of speciation and other historical factors in structuring natural communities. As examples of implications for understanding and eventually treating human diseases, because they exhibit parental care that is not complicated by the feeding of young, female rattlesnakes offer a simple model system for studying hormonal control of that behavior. Likewise, the shaker muscle anatomically and physiologically resembles heart tissue, and in recent years the tails of restrained, live rattlesnakes have proved extremely useful for studying muscle biochemistry in intact organisms with NMR and other in vivo techniques. Understanding rattlesnake evolutionary relationships will enable researchers to strategically choose species that have or lack particular characteristics, and thereby untangle the molecular mechanisms underlying the development of normal and abnormal functions.