Role of light and temperature in the regulation of reproduction in the red-sided garter snake, Thamnophis sirtalis parietalis

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The influence of photoperiodic manipulation on sexual behavior and ovarian recrudescence of male and female red-sided garter snakes (Thamnophis sirtalis parietalis) was examined over a 4-year period. Snakes were exposed to photoperiodic manipulations before, during, and after a 17-week cold temperature dormancy; sexual behavior of males and females and ovarian recrudescence were observed after emergence from cold temperature dormancy. In the 1st year (1982), males were exposed to two conditions representing minimum and maximum exposure to daylight: (i) 6 weeks of a short-day prehibernation period (10L:14D, 28:18 °C), followed by 17 weeks of hibernation in complete darkness (0L:24D, 4 °C) and emergence into warm dark conditions (0L:24D, 28:18 °C); and (ii) 6 weeks of a long-day prehibernation period (14L:10D, 28:18 °C), followed by 17 weeks of hibernation with exposure to light (12L:12D, 4 °C) and emergence into warm, long days (14L:10D, 28:18 °C). Males in both conditions exhibited intense courtship behavior on emergence from hibernation. Females in 1982 were significantly influenced only by long-day prehibernation conditions (14L:10D, 28:18 °C); under these conditions, ovarian recrudescence on emergence was inhibited. Long prehibernation photoperiod did not significantly influence female receptive behavior on emergence, indicating that neuroendocrine control of ovarian activation and sexual behavior may be separate in this species. In three subsequent years (1983, 1984, 1985) none of the photoperiodic conditions significantly influenced male or female sexual behavior or ovarian recrudescence. Slight differences in experimental protocol in these subsequent years that may account for differences in results from 1982 are discussed. Finally, ovarian development was found to be clearly tied to the duration of cold temperature dormancy in this species. Females receiving 7 or 17 weeks of exposure to cold (4 °C) underwent vitellogenesis at similar frequencies. Most females receiving 0 or only 4 weeks of exposure to cold (4 °C) did not become vitellogenic. Mating on emergence was not a requirement for the initiation of vitellogenesis in this study.