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Unformatted text preview: STRESS IN FREE-RANGING MAMMALS: INTEGRATING PHYSIOLOGY, ECOLOGY, AND NATURAL HISTORY D EE A NN M. R EEDER * AND K RISTIN M. K RAMER Department of Biology, Boston University, 5 Cummington Street, Boston, MA 02215, USA (DMR) The Brain–Body Center, Department of Psychiatry (MC 912), University of Illinois at Chicago, 1601 W Taylor Street, Chicago, IL 60612, USA (KMK) We review developments in the study of stress in free-ranging mammals and summarize the physiological and behavioral components of the stress response. Both the sympathetic nervous system response and the regulation and reactivity of the hypothalamic–pituitary–adrenal (HPA) axis are discussed. In particular, we describe how the activity of the HPA axis at baseline levels follows circadian and circannual rhythms in ways that allow animals to respond to predictable environmental changes, focusing largely on the endpoint of this axis, the glucocorticoid hormones cortisol and corticosterone. Superimposed upon these rhythms are the elevated glucocorticoid levels characteristic of the stress response, which allow an animal to respond to unpredictable social, physical, or environmental challenges. Methods used to explore the stress response in free-ranging mammals are described. Both inter- and intraspecific variation in the stress response as they relate to the environment are discussed. Finally, how the regulation and reactivity of the HPA axis varies by life-history stage and sex in mammals is reviewed, focusing on reproduction and development. Key words: corticosterone, cortisol, ecology, glucocorticoid, hypothalamic–pituitary–adrenal axis, natural history, physiology, mammals, stress Although the behavioral and physiological components of stress are well studied in a handful of laboratory mammals (especially muroid rodents and primates), our understanding of stress and its relevancy for an animal in its natural environment is rudimentary at best, and completely unknown at worst for the majority of the 5,416 species of mammals currently recognized (Wilson and Reeder, in press). Nevertheless, recent studies have begun to explore stress in free-ranging mammals. These studies often must incorporate and are in fact interested in the very factors that laboratory studies control for, such as environmental variation, variable reproductive condition and life history, and social influences. The emergence of these studies has been permitted by the development of techniques that are feasible in field settings and by the advent of new methods of quantifying stress, including techniques for noninvasive sampling of hor- monal indicators of stress. Because of the growing interest in stress as it relates to the natural history and ecology of mammals, we (Reeder and Kramer) organized a symposium, ‘‘ Stress in Nature: Impact on Physiology, Ecology, and Natural History of Mammals ’’ for the 83rd Annual Meeting of the American Society of Mammalo- gists, held in Lubbock, Texas, in June 2003. Specific objectivesgists, held in Lubbock, Texas, in June 2003....
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