Meeting Abstract
Wild animals often cope with stressful stimuli that elicit a suite of physiological and behavioral responses. One central element to these responses is upregulation of the hypothalamic-pituitary-adrenal (HPA) axis and corticosterone (CORT) release. The immune, metabolic, cardiovascular, and behavioral systems are also intricately involved during these responses. While many mechanisms are activated to cope with stress, a comprehensive model of these responses has yet to be thoroughly tested. The reactive scope model provides a framework to understand and simplify the complicated timing of stress by separating mediator levels into four distinct categories; (1) predictive homeostasis, (2) reactive homeostasis, (3) homeostatic failure, and (4) homeostatic overload. An assumption of this model is that exposure to layered, repeated stressful stimuli cause an animal to enter the overload region more rapidly than exposure to a single stressor alone. In this study, we used house sparrows (Passer domesticus) to test this hypothesis by assessing CORT, immune, metabolic, and behavioral responses. Birds were exposed to four days of one stressor, followed by four days of a second (layered/repeated) stressor. Maximal physiological CORT production and microbial killing capacity decreased after repeated stress exposure, responses that align with predictions from reactive scope. Uric acid and neophobic behavior decreased after presentation of the first stressor and remained low after the repeated stressor. Although a number of metrics did not change during the protocol, none of the observed responses were opposite to those predicted by reactive scope. Overall the results provide partial support for the model.
