Sexual conflict in the snake den

Red-sided garter snakes (Thamnophis sirtalis parietalis) court and mate in spring, soon after they emerge from large communal overwintering dens in so uth-central Manitoba. Because of a massive bias in the operational sex rati o, every female attracts intense courtship from dozens to hundreds of males . We suggest that this courtship constitutes significant "harassment," beca use it delays the females' dispersal from the den and hence increases their vulnerability to predation. Small females may face the greatest costs, bec ause they are less able to escape from amorous males (who court all females , even juvenile animals). Our measurements show that males are stronger and faster than females. Experimental trials confirm that the locomotor abilit y of ft males (especially small females) is greatly reduced by the weight o f a courting male. Arena trials show that intense courtship stimulates fema les to attempt to escape. Remarkably, some females that are too small to pr oduce offspring may nonetheless copulate. This precocious sexual receptivit y may benefit juvenile females because copulation renders them unattractive to males, and thus allows them to escape more easily from the den. Female "tactics" to escape male harassment may explain other puzzling aspects of g arter snake biology including size-assortative mating, temporal patterns in dispersal from the den, avoidance of communal dens by young-of-the-year sn akes, and female mimicry. Hence, sexual conflict may have influenced import ant features of the mating system and behavioral ecology of these animals.