Effects of Temperature on Sexual Receptivity and Ovarian Recrudescence in the Garter Snake, Thamnophis sirtalis parietalis

Exposure to low temperatures in darkness (hibernation) appears to be required for the induction of sexual receptivity and eventual vitellogenesis in female garter snakes Thamnophis sirtalis parietalis; the relative importance of temperature vs. light is unknown. Temperature, independent of photoperiod, may affect follicular condition. In snakes kept in the dark at 4 C or at 17 C with a 12L:12D photoperiod for up to 20 wk starting in fall, ovaries remained at the same size and previtellogenic condition characteristic of animals entering hibernation in autumn. In contrast, at 30 C with 12L:12D, snakes fed well and appeared healthy, but ovaries underwent complete regression which persisted for over a year; follicles involuted with a net loss in ovarian gonadotropin receptors. Females maintained at 17 C or 30 C (with only previtellogenic or regressed ovaries) remained sexually attractive to courting males for over a year, despite the absence of an ovarian cycle; those at 30 C, with the most regressed ovaries, were most attractive. However, with few exceptions, only snakes kept in simulated hibernation for 16 wk or more were sexually receptive, and only those that mated became vitellogenic. Thus, copulation appears to be an important prerequisite for the initiation of vitellogenesis in this snake, although ovaries did not develop in all mated females: small or estrogen-treated females remained previtellogenic after mating.