The implications of stress on male mating behavior and success in a sexually dimorphic polygynous mammal, the grey seal Damian C. Lidgard a,b, ⁎ , Daryl J. Boness b,c , W. Don Bowen d , Jim I. McMillan d a Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4JI b Conservation and Research Center, National Zoological Park, Smithsonian Institution, 3001 Connecticut Avenue NW, Washington, D.C. 20008-2598, USA c Department of Wildlife Ecology and School of Marine Science, University of Maine, Orono, ME, USA d Population Ecology Division, Bedford Institute of Oceanography, Department of Fisheries and Oceans, Dartmouth, Nova Scotia, Canada B2Y 4A2 Received 20 July 2007; revised 1 October 2007; accepted 3 October 2007 Available online 12 October 2007 Abstract Studies on primates and other taxa have shown that the physiological response of an individual to stress reflects their social status. We combined behavioral observations with measures of stress to test the hypothesis that stress is an important physiological determinant of mating behavior and success in the male grey seal. Known-age males (N = 19) were studied during the breeding seasons of 2004 and 2005 at Sable Island, Canada. The stressor was a capture and restraint period of 35 min and serial samples of cortisol and testosterone were taken as measures of stress. The mean baseline concentrations of cortisol and testosterone were 9.7 ± 0.5 ug/dl and 6.2 ± 0.6 ng/mL, respectively. The baseline cortisol concentration was negatively correlated with the duration of time a male spent at a site (r = - 0.507, P = 0.027), which was a strong correlate of mating success (r = 0.659, P = 0.002). All males experienced an increase in the concentration of cortisol during the restraint period (79.1 ± 8.4%; CV = 46.1%). The percentage rise in cortisol during restraint was correlated with the mean duration of time spent at a site (r = 0.544, P = 0.016) and thus success. The concentration of testosterone also increased during the restraint period (32.8 ± 9.7%). This might be an adaptive response to maintaining the ability to reproduce while under stress. Our study indicates that stress is an important determinant of success in male grey seals. More successful males might exhibit an adaptive response to stress by maintaining low concentrations of cortisol during breeding. © 2007 Elsevier Inc. All rights reserved. Keywords: Cortisol; Breeding behavior; Breeding success; Glucocorticoids; Pinniped; Seal; Stress; Testosterone Introduction Animals are faced with a diverse array of stressors during their lifetime. These may originate from the environment (e.g., population density, Rogovin et al., 2003) or from aspects of life history (e.g., breeding events, Abbott et al., 2003). Stressors can upset the physiological balance, or homeostasis of the indi- vidual and consequently affect growth, reproductive behavior, energetics, the immune system and survival (Bartsh et al., 1992; Boonstra et al., 1998; Creel, 2001; Jessop et al., 2002; Rogovin et al., 2003; Sapolsky, 2002). In vertebrates, the typical response to a stressor is a com- plicated cascade of physiological events that results in the release of glucocorticoids (e.g., cortisol) to ready the animal for a ‘fight or flight’ response (Sapolsky et al., 2000). Glucocorticoids are also involved in suppressing reproductive behavior which, in the case of males, occurs through several mechanisms that lead to a decrease in the concentration of testosterone (Sapolsky, 2002; Wingfield and Sapolsky, 2003). Several studies have shown that in some species the actions of glucocorticoids on reproductive function are suppressed during the breeding season as an adaptive response to allow individuals to reproduce in stressful environments (e.g., Silverin et al., 1997) or to maximize their success during a short breeding season (e.g., Astheimer et al., 2000). However, studies on primates and other taxa have shown that the magnitude of this suppression differs according to the individual's social status in the breeding group (Sapolsky, 1982; Creel, 2001; Abbott et al., 2003). In olive baboons (Papio anubis), males that have high copulatory success experience an increase in testosterone concentration during a stressful event Available online at www.sciencedirect.com Hormones and Behavior 53 (2008) 241 – 248 www.elsevier.com/locate/yhbeh ⁎ Corresponding author. Department of Biology, Dalhousie University, Halifax, Nova Scotia, Canada B3H 4JI. Fax: +1 902 494 3736. E-mail address: damian.lidgard@dal.ca (D.C. Lidgard). 0018-506X/$ - see front matter © 2007 Elsevier Inc. All rights reserved. doi:10.1016/j.yhbeh.2007.10.003