Meeting Abstract
Despite increasing evidence that glucocorticoids regulate life-history transitions, the mechanisms linking changing glucocorticoids to particular life events remain unclear. We studied the role of glucocorticoids in coordinating two key life-history transitions in garter snakes: spring and fall migration from and to the breeding site. In comparing our female data with previous work in males, we uncovered variation in stress responses with season, sex and migration state. We examined the mechanisms underlying this variation by assessing adrenal sensitivity to adrenocorticotropic hormone (ACTH). Males are less responsive to ACTH than females during the spring mating season, indicating that sex differences in stress responsiveness are related to modulation of adrenal sensitivity in males. Interestingly, pre-migratory, breeding females responded to and recovered from capture stress more quickly than migrating females, suggesting that negative feedback on the HPA axis may be linked to changes in female reproductive state. Females reproduce biennially and thus variation in reproductive history may be related to both stress sensitivity and energetic condition, leading us to probe the relationship between the HPA axis and reproductive condition. Mating behavior, but not stress responses, predicted whether a female reproduced during the summer. Stress responses did vary with receptivity however, suggesting that variation in the sensitivity of the HPA axis is related to whether a female will reproduce in a given year. These data collectively describe how HPA axis activity and sensitivity vary with season, sex, migration status and reproductive history. Our results support the hypothesis that the HPA axis coordinates the changes in physiology and behavior vital to transitioning between life-history events.
