Behavioural and hormonal responses to capture stress in the male red-sidedgarter snake, Thamnophis sirtalis parietalis

We measured the behavioural and hormonal responses to capture stress in mal e red-sided garter snakes. Four hours of capture stress resulted in no supp ression of mating behaviour relative to control individuals. In contrast, t he same stress resulted in a significant increase in plasma levels of corti costerone and a significant decrease in plasma levels of testosterone. Ther e was a significant negative correlation between plasma levels of corticost erone and testosterone in both control and capture-stress groups, suggestin g that the increase in corticosterone directly drives the decrease in testo sterone. While there was no relation between body size and initial plasma l evels of the two steroids, longer individuals had a significantly greater i ncrease in corticosterone following capture stress than did shorter individ uals. Snakes display indeterminate growth, suggesting that older individual s have decreased sensitivity to negative feedback in the hypothalamic-pitui tary-adrenal axis and thus hypersecrete glucocorticoids. These results sugg est that male red-sided garter snakes have uncoupled their behavioural stre ss response from their hormonal stress response to maximize reproductive op portunities. (C) 2000 The Association for the Study of Animal Behaviour.