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      Individual‐based analysis of hair corticosterone reveals factors influencing chronic stress in the American pika

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          Abstract

          Glucocorticoids are often measured in wildlife to assess physiological responses to environmental or ecological stress. Hair, blood, saliva, or fecal samples are generally used depending on the timescale of the stress response being investigated and species‐specific considerations. Here, we report the first use of hair samples to measure long‐term corticosterone levels in the climate‐sensitive American pika ( Ochotona princeps). We validated an immunoassay‐based measurement of corticosterone extracted from hair samples and compared corticosterone estimates obtained from plasma, hair, and fecal samples of nine pikas. To demonstrate an ecological application of this technique, we characterized physiological stress in 49 pikas sampled and released at eight sites along two elevational transects. Microclimate variation was measured at each site using both ambient and subsurface temperature sensors. We used an information theoretic approach to compare support for linear, mixed‐effects models relating corticosterone estimates to microclimate, body size, and sex. Corticosterone was measured accurately in pika hair samples after correcting for the influence of sample mass on corticosterone extraction efficiency. Hair‐ and plasma‐based estimates of corticosterone were weakly correlated. The best‐supported model suggested that corticosterone was lower in larger, male pikas, and at locations with higher ambient temperatures in summer. Our results are consistent with a general negative relationship between body mass and glucocorticoid concentration observed across mammalian species, attributed to the higher mass‐specific metabolic rates of smaller bodied animals. The higher corticosterone levels in female pikas likely reflected the physiological demands of reproduction, as observed in a wide array of mammalian species. Additionally, we establish the first direct physiological evidence for thermal stress in the American pika through nonlethal sampling of corticosterone. Interestingly, our data suggest evidence for cold stress likely induced during the summer molting period. This technique should provide a useful tool to researchers wishing to assess chronic stress in climate‐sensitive mammals.

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          Hair cortisol as a biological marker of chronic stress: current status, future directions and unanswered questions.

          The detrimental effects of stress on human health are being increasingly recognized. There is a critical need for the establishment of a biomarker that accurately measures its intensity and course over time. Such a biomarker would allow monitoring of stress, increase understanding of its pathophysiology and may help identify appropriate and successful management strategies. Whereas saliva and urine cortisol capture real-time levels, hair cortisol analysis presents a complementary means of monitoring stress, capturing systemic cortisol exposure over longer periods of time. This novel approach for cortisol quantification is being increasingly used to identify the effects of stress in a variety of pathological situations, from chronic pain to acute myocardial infarctions. Because of its ability to provide a long-term, month-by-month measure of systemic cortisol exposure, hair cortisol analysis is becoming a useful tool, capable of answering clinical questions that could previously not be answered by other tests. In this paper we review the development, current status, limitations and outstanding questions regarding the use of hair cortisol as a biomarker of chronic stress. Copyright © 2011 Elsevier Ltd. All rights reserved.
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            Do baseline glucocorticoids predict fitness?

            Baseline glucocorticoid (cort) levels are increasingly employed as physiological indices of the relative condition or health of individuals and populations. Often, high cort levels are assumed to indicate an individual or population in poor condition and with low relative fitness (the Cort-Fitness Hypothesis). We review empirical support for this assumption, and find that variation in levels of baseline cort is positively, negatively, or non-significantly related to estimates of fitness. These relationships between levels of baseline cort and fitness can vary within populations and can even shift within individuals at different times in their life history. Overall, baseline cort can predict the relative fitness of individuals and populations, but the relationship is not always consistent or present.
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              Use of fecal glucocorticoid metabolite measures in conservation biology research: considerations for application and interpretation.

              Fecal glucocorticoid metabolite analyses are increasingly being used by a variety of scientists (e.g., conservation biologists, animal scientists) to examine glucocorticoid (i.e., stress hormone) secretion in domestic and wild vertebrates. Adrenocortical activity (i.e., stress response) is of interest to conservation biologists because stress can alter animal behavior, reduce resistance to disease, and affect population performance. The noninvasiveness of fecal-based assessments is attractive, particularly when studying endangered species, because samples can often be obtained without disturbing the animal. Despite such advantages, many confounding factors inhibit the utility of this technique in addressing conservation problems. In particular, interpretation of fecal glucocorticoid metabolite (FGM) measures may be confounded by the length of time animals are held in captivity, normal seasonal and daily rhythms, body condition, sample storage and treatment techniques, diet of the animal, assay selection, animal status (i.e., social ranking, reproductive status), sample age and condition, and sample mass. Further complicating interpretation and utility of these measures is the apparent species-specific response to these factors. The purpose of this paper is to discuss the factors that confound interpretation of FGM measures, summarize research that addresses these issues, and offer an agenda for future research and interpretation. We urge conservation biologists to carefully consider confounding factors and the relationship between FGM secretion and population performance and biological costs when investigating effects of environmental and human-induced disturbances on wildlife. The crisis nature of many decisions in conservation biology often requires decisions from limited data; however, confirmatory results should not be posited when data are incomplete or confounding factors are not understood. Building reliable databases, and research with surrogate species when possible, will aid future efforts and enhance the utility of FGM assays.
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                Author and article information

                Contributors
                michael.russello@ubc.ca
                Journal
                Ecol Evol
                Ecol Evol
                10.1002/(ISSN)2045-7758
                ECE3
                Ecology and Evolution
                John Wiley and Sons Inc. (Hoboken )
                2045-7758
                26 April 2017
                June 2017
                : 7
                : 12 ( doiID: 10.1002/ece3.2017.7.issue-12 )
                : 4099-4108
                Affiliations
                [ 1 ] Department of BiologyUniversity of British Columbia Kelowna BCCanada
                [ 2 ] Institute of Arctic and Alpine Research and Department of Ecology and Evolutionary Biology University of Colorado Boulder COUSA
                [ 3 ] Departments of Biology and Environmental StudiesWarren Wilson College Asheville NCUSA
                Author notes
                [*] [* ] Correspondence

                Michael A. Russello, Department of Biology, University of British Columbia, Kelowna, BC, Canada.

                Email: michael.russello@ 123456ubc.ca

                Author information
                http://orcid.org/0000-0002-9297-2485
                Article
                ECE33009
                10.1002/ece3.3009
                5478070
                28649323
                7ee316a0-a5b1-473f-931c-8385b0da3c66
                © 2017 The Authors. Ecology and Evolution published by John Wiley & Sons Ltd.

                This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited.

                History
                : 22 August 2016
                : 20 January 2017
                : 26 March 2017
                Page count
                Figures: 5, Tables: 3, Pages: 10, Words: 8647
                Funding
                Funded by: Natural Sciences and Engineering Research Council of Canada
                Award ID: # 341711
                Categories
                Original Research
                Original Research
                Custom metadata
                2.0
                ece33009
                June 2017
                Converter:WILEY_ML3GV2_TO_NLMPMC version:5.1.1 mode:remove_FC converted:20.06.2017

                Evolutionary Biology
                body mass,climate change,glucocorticoids,mammal,metabolic rate,thermal stress,wildlife

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