To avoid or not to avoid? Factors influencing the discrimination of predator diet cues by a terrestrial salamander

Many prey species use chemical cues deposited by predators to assess predation risk, and some prey are capable of discriminating among predator chemical traces based on the predator's recent diet. Here we test the influence of genetic relatedness (degree of genetic similarity between prey) and ecological relatedness (degree of refuge and trophic overlap between syntopic prey) on the evolution of predator-diet discrimination by red-backed salamanders, Plethodon cinereus. In experiment 1, we examined whether red-backed salamanders from Binghamton University (Binghamton, New York, U.S.A.) would differentially respond to chemical traces from garter snakes ( Thamnophis sirtalis) fed conspecific P. cinereus from four populations belonging to three phylogenetic groups: Group II from Mountain Lake, Virginia, Group III from Binghamton University, New York, Group III from Hawk Mountain, Pennsylvania, and Group IV from Cherry Springs, Pennsylvania, U.S.A. The test salamanders only avoided chemical traces from garter snakes fed salamanders from the two Group III sites, although the response to the Group III-Hawk Mountain treatment was intermediate to that for the Group III-Binghamton University treatment and the Group II and IV treatments. In experiment 2, we examined whether red-backed salamanders collected from two subpopulations, syntopic or allotopic with two-lined salamanders, Eurycea bislineata, vary in their response to chemical cues from garter snakes foraging on two-lined salamanders. Only red-backed salamanders syntopic with E. bislineata avoided chemical traces from garter snakes fed E. bislineata. These results suggest that both genetic and ecological relatedness play a role in the evolution of predator-diet discrimination in red-backed salamanders.