Meeting Abstract
Evolutionary trade-offs are predicted to arise when a locally adapted allele exhibits antagonistic effects in a foreign environment. Genetic polymorphism will then be maintained among populations that experience divergent patterns of selection across a heterogeneous landscape. We tested for trade-offs at a polymorphic locus of large-effect that determines toxin resistance in populations of the common garter snake (Thamnophis sirtalis). Two separate lineages of T. sirtalis in western North America independently evolved changes to the skeletal muscle sodium channel (NaV1.4) that confer resistance to tetrodotoxin (TTX) in their prey, Pacific newts (Taricha spp.). In California populations, we found that homozygous snakes with a highly resistant allele of the NaV1.4 channel had a slower average crawl speed than individuals with the ancestral, TTX-sensitive channel. Previous molecular work indicates the same TTX-resistant mutations have pleiotropic effects on a range of important biophysical properties of the NaV1.4 channel. A negative relationship between TTX resistance and locomotor performance suggests trade-offs could maintain polymorphism in the NaV1.4 channel of T. sirtalis across the geographic mosaic of variably toxic newt populations.
