Department of Ecology & Evolutionary Biology, University of California, 621 Charles E. Young Drive South, Los Angeles, CA 90095-1606, USA.
Gen Comp Endocrinol. 2012 Sep 1;178(2):417-26. doi: 10.1016/j.ygcen.2012.06.015. Epub 2012 Jun 23.
Natural selection is expected to shape phenotypic traits that permit organisms to respond appropriately to the environments in which they live. One important mechanism by which animals cope with changes in their environment is through physiological responses to stressors mediated by glucocorticoid hormones. Here we perform biological and physiological validations of a minimally-invasive technique for assessing fecal corticosterone metabolites (FCMs) in captive and wild groups of yellow-bellied marmots (Marmota flaviventris). Then we draw from ten years of data on these obligate hibernators at the Rocky Mountain Biological Laboratory in Colorado, USA to assess the extent to which seasonal and daily changes explain naturalistic variation in baseline levels of FCMs. Interestingly, beyond important population-level variation with respect to year, season, time of day, sex, age and reproductive state, we found repeatable inter-individual differences in FCMs, suggesting this hormonal trait might be a meaningful target of selection. FCM levels were 68% lower in captive than wild marmots, suggesting that the natural environment in which these animals occur is generally more challenging or less predictable than life in captivity. Most live-trapping events failed to represent stressors for wild marmots such that repeated measurements of traits were possible with minimal "stress" to subjects. We also document the natural ranges of annual and seasonal variation necessary for understanding the extent to which anthropogenic assaults represent stressors for wild mammals. Taken together, this study provides a foundation for understanding the evolution of hormonal traits and has important welfare and conservation implications for field biologists.
自然选择有望塑造出使生物能够适应其生活环境的表型特征。动物应对环境变化的一个重要机制是通过糖皮质激素介导的生理应激反应。在这里，我们对一种评估圈养和野生黄腹土拨鼠（Marmota flaviventris）粪便皮质酮代谢物（FCM）的微创技术进行了生物学和生理学验证。然后，我们利用美国科罗拉多落基山生物实验室十年来对这些冬眠动物的数据，评估季节性和日常变化在多大程度上解释了 FCM 基线水平的自然变异。有趣的是，除了与年份、季节、一天中的时间、性别、年龄和繁殖状态有关的重要群体水平变异外，我们还发现 FCM 存在可重复的个体间差异，这表明这种激素特征可能是选择的一个有意义的目标。圈养土拨鼠的 FCM 水平比野生土拨鼠低 68%，这表明这些动物生活的自然环境通常比圈养环境更具挑战性或不可预测。大多数活体诱捕事件都不能代表野生土拨鼠的应激源，因此可以在对实验对象最小“应激”的情况下进行多次测量。我们还记录了年度和季节性变化的自然范围，这对于理解人为攻击对野生哺乳动物构成的应激源的程度至关重要。总之，这项研究为理解激素特征的进化提供了基础，对野外生物学家具有重要的福利和保护意义。
