Assessing adaptive and maladaptive stress responses in wild Capuchin monkeys

Stress is a problem that affects millions of people and animals across the globe every day. Most studies on the impacts of stress use a biomedical perspective and focus on its negative, non-adaptive effects on health. In contrast, studies based in behavioral ecology assess how stress responses can adaptively rescue organisms from challenges. The dichotomy established by these two approaches limits our understanding of stress because stresses that originally trigger an adaptive response may in time take a cumulative toll resulting in wear-and-tear (reduced longevity) or chronic stress (inability to elicit an adaptive response). To advance knowledge about stress reactivity in general, and social reactivity in particular, this study analyzes two populations of a wild primate that have been naturally exposed to different environmental (natural periods of food restriction) and social (overcrowding) stresses. This comparison offers a powerful tool for detecting how variation in stress responses relate to individual health and fitness. The research develops outreach activities for grade-school children, builds capacity at the field laboratory, and contributes to conservation efforts. This research is the first to make unprecedented gains in understanding the adaptive and maladaptive nature of the stress response in wild primates. The study focuses on 120 wild capuchins living in two different forests to: (1) measure the variation in glucocorticoids before and after known social (e.g., aggression between neighboring groups) and ecological stressors (e.g., droughts); (2) quantify each individual’s unique stress response; (3) determine whether these responses are repeatable; (4) determine if the same individuals respond differently to different stressors and/or if the same stressor induces different responses from different individuals, and; (5) assess which if any stress responses have fitness consequences. The study uses a within-subject approach by measuring fine-scale variation in fecal stress hormones (glucocorticoids) before and after facing a known stressor. The data generated builds a baseline for stress-induced hormone levels against which the levels associated with stress-reaction can be compared. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.