Ovarian development in red-sided garter snakes, Thamnophis sirtalis parietalis: relationship to mating.

Female red-sided garter snakes (Thamnophis sirtalis parietalis) exhibit a complex array of behavioral patterns. Females may mate once, more than once, or not at all in the spring of the year, and a high percentage of females may mate in late summer before returning to winter hibernacula. The role of mating in the induction of ovarian growth in this species is complicated by this pattern of spring and late summer mating. Females hibernated in the laboratory that mate on emergence in the spring exhibit higher frequencies of ovarian recrudescence than females that do not mate when exposed to males. Yet neither male courtship nor mating in the spring is required for ovarian development. However, mated and unmated females collected in the field in the spring of the year do not differ in frequencies of ovarian recrudescence. Ovarian growth in unmated females collected in the spring parallels the incidence of mating in the previous late summer. Thus, mating may influence the initiation of ovarian growth, but the effect can occur immediately (from spring mating) or be stored over winter (from late summer mating). Large year-to-year variation in reproductive rates of female red-sided garter snakes suggests that other factors such as nutrition and stored energy reserves may modify the effects of mating on ovarian growth.