Collaborative Research: Independent Evolutionary Origins of Tetrodotoxin Resistance as a Test of the Geographic Mosaic of Coevolution

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The proposed research will investigate the role of geographic structure in determining patterns of coevolutionary interaction and the dynamics of arms-races. It has been difficult in the past to disentangle biogeographic structure itself from the environmental differences among populations because study systems cannot be replicated within the same geographic range. The arms race between garter snakes of the genus Thamnophis and toxic newts of the genus Taricha provides a unique opportunity to explore this problem because new evidence indicates multiple independent evolutionary origins of the traits critical to the interaction. The proposed research will determine the broad-scale geographic patterns of variation in tetrodotoxin toxicity and sodium channel resistance in regions where multiple species of garter snakes and newts occur. If geography and/or prey phenotypes are most important in determining coevolutionary trajectories, sympatric populations of garter snakes will show matched levels of resistance. If differences in the selective environment or species interactions are paramount, then sympatric populations of predators will have unmatched levels of resistance. By surveying diet composition in sympatric predators and the degree of phenotype matching between each predator and prey species, the investigators can further determine the general factors influencing mismatches among sympatric predators. Revealing the fundamental aspects of coevolution is critical to furthering our understanding of all biological interactions, whether they occur between humans and pathogens, disease and antibiotics, or predators and prey. This project explores basic elements of the coevolutionary process that impact all systems. The proposed funding will directly support the training of two graduate students as research assistants as well as numerous other graduate and undergraduate students that are involved with the project at all levels. The snake-newt arms race has developed as a popular paradigm for understanding coevolution through outreach education (on recent PBS-TV, popular press, and a coming exhibit in the Wonderlab children's science museum in Bloomington, IN).