Responses to capture stress and exogenous corticosterone vary with body condition in female red-sided garter snakes (Thamnophis sirtalis parietalis)

This study examined whether hormonal and behavioral responses to capture stress and exogenous corticosterone (CORT) vary with body condition in female red-sided garter snakes (Thamnophis sirtalis parietalis). Female snakes were collected during the spring mating season and treated with 4 h of capture stress. We measured plasma CORT and estradiol before, during and after capture stress treatment followed by latency to copulate, a measure of female receptivity. Body condition was determined as the residual from a regression of body mass on snout-vent-length. Baseline CORT did not differ between females in positive and negative body condition, but females in negative body condition showed a significantly larger increase in plasma CORT in response to capture stress. Estradiol, which is generally low during the mating season in this population, did not change in response to capture stress. Body condition, but not capture stress, influenced latency to copulate, suggesting that females are resistant to the behavioral effects of capture stress during the spring mating season. In a second experiment, only females in negative body condition increased latency to copulate in response to injection of a physiological (15 μg) dose of exogenous CORT, while all females responded to a pharmacological (60 μg) dose. These results indicate that behavioral responses to exogenous CORT vary with female body condition during the short mating season. Taken together, our data suggest that variation in body condition may be associated with differences in HPA axis sensitivity and/or glucocorticoid receptor density in the brain.