Male red-sided garter snakes, Thamnophis sirtalis parietalis, determine female mating status from pheromone trails

Recently mated females of some species experience a refractory period following mating during which a physiological change or a mating plug prevents remating. Males that determine female mating status from a distance will minimize time spent searching for mates by avoiding unavailable females. Female red-sided garter snakes experience a refractory period after mating due to a mating plug. Female garter snakes leave pheromone trails, which males detect and follow to find potential mates. We investigated the ability of male garter snakes to determine the mating status of females based solely on these pheromone trails. Males were given a choice between following two trails on a Y maze to examine whether they discriminate between mated and unmated females, whether this discrimination is based on changes in the sex-attractiveness pheromone or the copulatory fluids, and whether they continue to discriminate after the mated females have lost their mating plug. We found that male garter snakes discriminate between the trails of mated and unmated females. This discrimination is based on the presence of a copulatory pheromone, rather than changes in the sex-attractiveness pheromone. The duration of the copulatory pheromone coincides with the duration of the mating plug. Thus, male garter snakes are able to minimize time spent searching for unavailable females by determining female mating status from a distance.