Role of the Pineal Gland in the Control of Annual Reproductive Behavioral and Physiological Cycles in the Red-Sided Garter Snake (Thamnophis sirtalis parietalis)

Abstract

Red-sided garter snakes (Thamnophis sirtalis parietalis) exhibit a dissociated re productive pattern in nature: Male snakes court and mate with females after emergence from hibernation, when the gonads are regressed and not producing gametes or sex steroid hor mones. The proximate environmental cues used for timing this behavior appear to be the onset of warm ambient temperatures after prolonged exposure to cold temperatures. Pinealectomy blocks the normal onset of vernal courtship behavior in red-sided garter snakes. In the present study, snakes captured in the spring or the fall were pinealectomized in different seasons (i.e., spring or fall) prior to the onset of hibernation. Upon emergence, only 1 of 36 sham-operated animals failed to exhibit courtship behavior; 4 of 29 pinealectomized animals exhibited some courtship behavior, but none reached criterion. No animals courted 18 weeks after emer gence, and plasma testosterone levels were similar in pinealectomized and sham-operated animals, indicating that pinealectomy did not simply rephase courtship behavior in these snakes. Although some animals lost mass while others gained mass over the course of the study, this variable does not account for the absence of mating behavior in pinealectomized garter snakes. These data lend additional support to the hypothesis that the pineal gland directly influences reproductive behavior in the red-sided garter snake.