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      Endocrine rhythms in the brown bear (Ursus arctos): Evidence supporting selection for decreased pineal gland size

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          Many temperate zone animals adapt to seasonal changes by altering their physiology. This is mediated in large part by endocrine signals that encode day length and regulate energy balance and metabolism. The objectives of this study were to determine if the daily patterns of two important hormones, melatonin and cortisol, varied with day length in captive brown bears (Ursus arctos) under anesthetized and nonanesthetized conditions during the active (March–October) and hibernation periods. Melatonin concentrations varied with time of day and season in nonanesthetized female bears despite exceedingly low nocturnal concentrations (1–4 pg/mL) in the active season. In contrast, melatonin concentrations during hibernation were 7.5-fold greater than those during the summer in anesthetized male bears. Functional assessment of the pineal gland revealed a slight but significant reduction in melatonin following nocturnal light application during hibernation, but no response to beta-adrenergic stimulation was detected in either season. Examination of pineal size in two bear species bears combined with a phylogenetically corrected analysis of pineal glands in 47 other species revealed a strong relationship to brain size. However, pineal gland size of both bear species deviated significantly from the expected pattern. Robust daily plasma cortisol rhythms were observed during the active season but not during hibernation. Cortisol was potently suppressed following injection with a synthetic glucocorticoid. The results suggest that melatonin and cortisol both retain their ability to reflect seasonal changes in day length in brown bears. The exceptionally small pineal gland in bears may be the result of direct or indirect selection.

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              GEIGER is a new software package, written in the R language, to describe evolutionary radiations. GEIGER can carry out simulations, parameter estimation and statistical hypothesis testing. Additionally, GEIGER's simulation algorithms can be used to analyze the statistical power of comparative approaches. This open source software is written entirely in the R language and is freely available through the Comprehensive R Archive Network (CRAN) at

                Author and article information

                Physiol Rep
                Physiol Rep
                Physiological Reports
                Blackwell Publishing Ltd
                August 2013
                22 August 2013
                : 1
                : 3
                [1 ]Departments of Integrative Physiology and Neuroscience, College of Veterinary Medicine, Washington State University Pullman, Washington, 99164
                [2 ]Veterinary Clinical Sciences, College of Veterinary Medicine, Washington State University Pullman, Washington, 99164
                [3 ]School of the Environment, Washington State University Pullman, Washington, 99164
                [4 ]School of Biological Sciences, Washington State University Pullman, Washington, 99164
                [5 ]Department of Biological Sciences, University of Idaho Moscow, Idaho, 83844
                Author notes
                Heiko T. Jansen, Department of IPN, 205 VBRB, Washington State University, Pullman, WA 99164. Tel: 509-335-7056 Fax: 509-335-4650E-mail: heiko@

                Funding Information Funding was provided by the Interagency Grizzly Bear Committee and the following Washington State University endowments: Raili Korkka Brown Bear Fund, Bear Research and Conservation Fund, and Nutritional Ecology Fund.

                © 2013 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society

                Re-use of this article is permitted in accordance with the Creative Commons Deed, Attribution 2.5, which does not permit commercial exploitation.

                Original Research

                brown bear, cortisol, melatonin, pineal, seasonal


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