Sexual conflict in the snake den

摘要

Red-sided garter snakes (Thamnophis sirtalis parietalis) court and mate in spring, soon after they emerge from large communal overeintering dens in south-central Manitoba. Because of a massive bias in the operational sex ratio, every female attractsintense courtship from dozens to hundreds of males. We suggest that this courtship constitutes significant "harassment," because it delays the females' dispersal from the den and hence increases their vulnerability to predation. Small females may face the greatest cost, because 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 ability of females (especially small females) is greatly reduced by the weight of a courting male. Arena trials show that intense courship stimulates females to attempt to escarp. Remarkably, some females that are too small to produce offspring may nonetheless copulate. This precocious sexual receptivity 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 garter snake biology including sizeassortative mating, temporal patterns in dispersal from the den, avoidance of communal dens by young-of-the-year snakes, and female mimicry. Hence, sexual conflict may have influenced important features of th mating system and behavioral ecology of these animals.