ANIMAL BEHAVIOUR, 2000, 59, 529–534 doi:10.1006/anbe.1999.1344, available online at http://www.idealibrary.com on Behavioural and hormonal responses to capture stress in the male red-sided garter snake, Thamnophis sirtalis parietalis IGNACIO T. MOORE, MICHAEL P. LEMASTER & ROBERT T. MASON Department of Zoology, Oregon State University (Received 7 May 1999; initial acceptance 12 June 1999; final acceptance 8 November 1999; MS. number: A8290R) We measured the behavioural and hormonal responses to capture stress in male red-sided garter snakes. Four hours of capture stress resulted in no suppression of mating behaviour relative to control individuals. In contrast, the same stress resulted in a significant increase in plasma levels of corticosterone and a significant decrease in plasma levels of testosterone. There was a significant negative correlation between plasma levels of corticosterone and testosterone in both control and capture-stress groups, suggesting that the increase in corticosterone directly drives the decrease in testosterone. While there was no relation between body size and initial plasma levels of the two steroids, longer individuals had a significantly greater increase in corticosterone following capture stress than did shorter individuals. Snakes display indeterminate growth, suggesting that older individuals have decreased sensitivity to negative feedback in the hypothalamic–pituitary–adrenal axis and thus hypersecrete glucocorticoids. These results suggest that male red-sided garter snakes have uncoupled their behavioural stress response from their hormonal stress response to maximize reproductive opportunities.  2000 The Association for the Study of Animal Behaviour During the breeding season, the hormonal and behav- ioural responses of an animal to a stressor are dependent on many factors including the individual’s reproductive state and the environment it inhabits (Greenberg & Wingfield 1987; Wingfield 1988, 1994; Moore et al. 1991; Wingfield et al. 1992; Dunlap & Wingfield 1995). The hormonal stress response is typically seen as an increase in plasma glucocorticoid hormones (corticosterone in rep- tiles), while the behavioural response can be manifested as suppression of reproductive behaviours (Greenberg & Wingfield 1987). This generalized reproductive sup- pression occurs primarily because of negative inter- actions between the hypothalamic–pituitary–adrenal (HPA) axis, responsible for glucocorticoid release, and the hypothalamic–pituitary–gonadal (HPG) axis, responsible for sex steroid release (Greenberg & Wingfield 1987; Rivier & Rivest 1991). Where reproductive opportunities are limited, some animals will suppress their stress response (Wingfield et al. 1992, 1995). Although suppressing sensi- tivity or activity of the HPA axis could increase mortality, in some environments the benefit of increased reproduc- tive success outweighs this potential cost (Wingfield et al. 1998). Most reptiles studied to date respond to capture stress and short-term confinement with increases in plasma corticosterone levels (reviewed by Lance 1990; Tyrrell & Cree 1998) and decreases in plasma testosterone (Moore et al. 1991; Knapp & Moore 1995, 1997). No studies in reptiles have investigated both the hormonal and behav- ioural effects of stress on reproduction. However, an amphibian, the rough-skinned newt, Taricha granulosa, has served as a model for understanding the behavioural effects of stress and corticosterone on reproductive behav- iour. Short-term stress as well as exogenous corticosterone have been demonstrated to suppress reproductive behav- iour directly (Moore & Miller 1984). We used an esti- mated effect size for the suppressive effects of capture stress on mating behaviour from Moore & Miller (1984) to investigate whether the male red-sided garter snake shows a similar suppression of reproductive behaviour in response to capture stress. Because of its unique life history in Manitoba, Canada, the red-sided garter snake is a good model for investi- gating adaptations of the stress response. It has a short 4-month activity period each year followed by 8 months of winter dormancy. Mating occurs immediately upon emergence in the spring, in large mating balls of up to 100 males courting a single female, while plasma sex steroid levels are decreasing, gonads are regressed and glucocorticoid levels are elevated (Crews et al. 1984; Krohmer et al. 1987; Whittier et al. 1987). We Correspondence and present address: I. T. Moore, Department of Zoology, Box 351800, University of Washington, Seattle, WA 98195, U.S.A. (email: moore@zoology.washington.edu). M. P. LeMaster and R. T. Mason are at the Department of Zoology, 3029 Cordley Hall, Oregon State University, Corvallis, Oregon 97331, U.S.A. 0003–3472/00/030529+06 $35.00/0  2000 The Association for the Study of Animal Behaviour 529