Intra-individual variability in fecal cortisol metabolites varies with lifetime exploration and reproductive life history in eastern chipmunks (Tamias striatus)
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Understanding the mechanistic links between individual variation in life history and behavior is a major challenge in evolutionary ecology. Glucocorticoids (GC) play a major role in this link through their baseline levels into the blood and their implication in stress responses to environmental perturbations. However, very few studies have investigated the long-term joint relationships between GC stress reactivity, life history, and behavior in natural conditions. Here, we took advantage of the behavioral and life history differences among individual males and females of a wild population of eastern chipmunks (Tamias striatus): We investigated how individual exploration, age, and reproduction were linked to level and intra-individual variability (IIV) of fecal cortisol metabolites over a 5-month period. Our analyses revealed that female cortisol levels decreased during gestation and lactation compared with non-reproductive females. We also found that slower exploring females and females with a smaller litter displayed higher IIV in fecal cortisol metabolites. For males, fecal cortisol metabolites level during the mating season increased with the number of offspring produced and decreased with age. Our study highlights the necessity of considering simultaneously seasonal fluctuations in GC level and the dynamics of stress reactivity in the study of life history and behavioral co-adaptations within natural populations.
KeywordsIntra-individual variability Alternative life histories Coping style Glucocorticoids Mate search Stress response
We thank Nature Conservancy of Canada and Ruiter Valley Land Trust for access to study site. We also thank Hélène Presseault-Gauvin for valuable assistance during the fecal cortisol metabolites assays and all graduate students and research assistants that have contributed to the data collection. The authors also thank William Vickery, Albrecht Schulte-Hostedde, Jean-François Giroux, and two anonymous reviewers for comments on a previous version of this manuscript. This work was funded by Natural Sciences and Engineering Research Council of Canada Discovery Grants (DG, DR, and FP) and Canada Research Chairs program (DR and FP) and by a team research project grant from the Fonds Québécois de la Recherche sur la Nature et les Technologies (DR, DG, Murray Humphries, Don Kramer, and the late Don Thomas). POM was supported by a scholarship from the Fonds Québécois de la Recherche sur la Nature et les Technologies. The authors declare no conflict of interest.
All manipulations, captures, and tests were conducted following the guidelines of the Canadian Council on Animal Care via Université du Québec at Montréal (permit numbers CIPA 0603-462-0607 and 0507-613-0509).
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