title: Seasonal variation in the degu (Octodon degus) endocrine stress response.
abstract: Many wild animals show seasonal variation in circulating levels of stress hormones. Seasonal changes in the stress response may help animals better cope with the different challenges faced during each life history stage. We determined the seasonal stress profile of wild, free-living degus in Chile. Female degus were sampled during non-breeding (January), mating/early gestation (July), late gestation (August), and lactation (1st litter-September, 2nd litter-January). Male degus were sampled during the first three time-points. We measured baseline cortisol (CORT), stress-induced CORT, and negative feedback efficacy using a dexamethasone suppression test. While we found that neither males nor females showed seasonal variation in baseline CORT or negative feedback levels, we did find significant seasonal variation in stress-induced CORT levels of both sexes. Male stress-induced CORT was lowest during mating while female stress-induced CORT was highest during late gestation and lactation. Overall, females had higher stress-induced CORT compared to males. Our data suggest that stress-induced levels of CORT are highest during periods with increased chance of stressor exposure or times of positive energy balance. Consequently, CORT responses to stress appear to be regulated according to different life history needs.
authors: Department of Biology, Tufts University, Medford, MA, USA. Electronic address: Carolyn.Bauer@tufts.edu.
authors: Carolyn M
authors: CM
authors: Bauer
authors: Department of Biological and Environmental Sciences, University of Tennessee at Chattanooga, TN, USA.
authors: Loren D
authors: LD
authors: Hayes
authors: Departamento de Ecología, Facultad de Ciencias Biológicas, Pontificia Universidad Católica de Chile, Santiago, Chile.
authors: Luis A
authors: LA
authors: Ebensperger
authors: Department of Biology, Tufts University, Medford, MA, USA.
authors: L Michael
authors: LM
authors: Romero
mesh_terms: D000818:Animals; D000835:Animals, Wild; D001947:Breeding; D002980:Climate; D004703:Endocrine System / Q000502:physiology*; D004734:Energy Metabolism / Q000502:physiology; D025461:Feedback, Physiological / Q000502:physiology; D005260:Female; D005938:Glucocorticoids / Q000097:blood; D006801:Humans; D006854:Hydrocortisone / Q000097:blood*; D007774:Lactation / Q000502:physiology; D008297:Male; D046329:Octodon / Q000502:physiology*; D012098:Reproduction / Q000502:physiology; D012621:Seasons; D012727:Sex Characteristics; D013312:Stress, Physiological / Q000502:physiology*
chemical_list: D005938:Glucocorticoids; D006854:Hydrocortisone
keywords: Baseline CORT; Cortisol; Negative feedback; Stress-induced CORT; The Energy Mobilization Hypothesis; The Preparative Hypothesis