Multiple paternity in the western terrestrial garter snake, Thamnophis elegans

Multiple paternity may be a widespread phenomenon in snakes, but studies to date are inadequate for assessing the effect that phylogeny may have on paternity. Hypothetical mechanisms responsible for polyandry in snakes include intersexual conflicts and avoidance of genetic incompatibilities due to inbreeding. We analysed the offspring of six litters of western terrestrial garter snakes (Thamnophis elegans (Baird and Girard, 1853)) using microsatellite DNA polymorphisms. We directly detected multiple paternity in half of the litters, one of which exhibited triple paternity, and substantial skew of paternal contributions in all multiply sired litters. Females producing multiply sired offspring were heavier postpartum and produced larger litters, suggesting that larger females that invest more in reproduction are more likely to be multiply mated, a result supporting the hypothesis that polyandry is due to intersexual conflict. Continued investigations of paternity patterns within this genus are under way, but if the factors driving polyandry in snakes are to be identified, controlled laboratory crosses are required.