50.2 Saturday, Jan. 5 Evolutionary history of tetrodotoxin-resistant sodium channels in snakes MCGLOTHLIN, J. W.*; FELDMAN, C. R.; BRODIE, JR., E. D.; PFRENDER, M. E. ; BRODIE III, E. D.; Virginia Tech; University of Nevada, Reno; Utah State University; University of Notre Dame; University of Virginia email@example.com
The garter snake Thamnophis sirtalis and its prey, the toxic newt Taricha granulosa, appear to be engaged in a coevolutionary arms race in western North America, with snakes evolving ever greater resistance to increasing levels of tetrodotoxin (TTX) in newts. On a molecular level, resistance in garter snakes derives from amino acid substitutions in voltage-gated sodium channels (Nav1.x, a family of 9 proteins found in excitable tissue), that prevent TTX from binding and and thus blocking ion flow. Populations of western Th. sirtalis that vary in resistance vary in the genotype of skeletal muscle sodium channels (Nav1.4), indicating an ongoing arms-race at that locus. We have recently discovered parallel evolution of signatures of resistance in two other channels, Nav1.6 and Nav1.7, which are found primarily in peripheral nerves. Here, we trace the evolutionary history of these genes in Thamnophis snakes and their relatives. Our results suggest that resistant nerves predate resistant muscles, perhaps predisposing garter snakes and their relatives to escalating coevolutionary arms races with toxic prey.