Meeting Abstract
Many animals exhibit seasonal changes in life-history stages that are often accompanied by dramatic switches in behavior. For example, migration is frequently accompanied by transitions between reproduction and feeding. While the neuroendocrine mechanisms that regulate such behavioral transitions are poorly understood, arginine vasotocin (AVT) and neuropeptide Y (NPY) are excellent candidates: brain AVT modulates reproductive behavior while NPY regulates feeding. We asked if seasonal changes in AVT and NPY are concomitant with migration to and from the breeding grounds in red-sided garter snakes (Thamnophis sirtalis). We collected male and female snakes pre- and post-migration during the spring and fall. Brains were processed for immunohistochemistry and the total number of AVT- and NPY-immunoreactive (ir) cells was counted and corrected for variation in regional brain volume. As predicted, males had significantly more AVT-ir cells in the preoptic area and bed nucleus of the stria terminalis during the spring mating season. Males had significantly more NPY-ir cells during the fall in the cortex and posterior hypothalamus, likely reflecting increased feeding behavior during the summer foraging period. Surprisingly, females did not exhibit seasonal differences in NPY-ir cell number, but did have more AVT-ir cells in the preoptic area during the spring. Neither AVT- nor NPY-ir cell number varied significantly with migratory status, although we did observe significant changes related to behavioral status (reproductive vs. nonreproductive). Our results suggest that AVT and NPY play a role in regulating seasonal transitions in reproductive and foraging behaviors, and may be involved in mediating sex differences in the timing of life-history events.
