Jebb Alexandra H M, Blumstein Daniel T, Bize Pierre, Martin Julien G A
School of Biological Sciences University of Aberdeen Aberdeen UK.
The Rocky Mountain Biological Laboratory Crested Butte CO USA.
Ecol Evol. 2021 Mar 9;11(7):3435-3445. doi: 10.1002/ece3.7304. eCollection 2021 Apr.
Body mass is often viewed as a proxy of past access to resources and of future survival and reproductive success. Links between body mass and survival or reproduction are, however, likely to differ between age classes and sexes. Remarkably, this is rarely taken into account in selection analyses. Selection on body mass is likely to be the primary target accounting for juvenile survival until reproduction but may weaken after recruitment. Males and females also often differ in how they use resources for reproduction and survival. Using a long-term study on body mass and annual survival in yellow-bellied marmots (), we show that body mass was under stabilizing viability selection in the first years of life, before recruitment, which changed to positive directional selection as age increased and animals matured. We found no evidence that viability selection across age classes on body mass differed between sexes. By investigating the link between running speed and body mass, we show that the capacity to escape predators was not consistent across age classes and followed a quadratic relationship at young ages only. Overall, our results indicate that mature age classes exhibit traditional patterns of positive viability selection on body mass, as expected in a hibernating mammal, but that mass in the first years of life is subjected to stabilizing selection which may come from additional predation pressures that negate the benefits of the largest body masses. Our study highlights the importance to disentangle selection pressures on traits across critical age (or life) classes.
体重常被视为过去获取资源以及未来生存和繁殖成功的一个指标。然而，体重与生存或繁殖之间的联系在不同年龄组和性别之间可能存在差异。值得注意的是，在选择分析中很少考虑到这一点。对体重的选择可能是影响幼体直至繁殖期生存的主要因素，但在幼体加入种群后可能会减弱。雄性和雌性在如何利用资源进行繁殖和生存方面也常常存在差异。通过对黄腹旱獭体重和年度生存情况的长期研究，我们发现，在幼体加入种群之前的生命最初几年里，体重受到稳定的生存力选择，随着年龄增长和动物成熟，这种选择转变为正向的定向选择。我们没有发现证据表明不同年龄组对体重的生存力选择在性别之间存在差异。通过研究奔跑速度与体重之间的联系，我们发现逃避捕食者的能力在不同年龄组并不一致，仅在幼年时呈二次关系。总体而言，我们的结果表明，成熟年龄组对体重表现出传统的正向生存力选择模式，这在冬眠哺乳动物中是预期的，但生命最初几年的体重受到稳定选择，这可能来自额外的捕食压力，抵消了最大体重带来的好处。我们的研究强调了区分关键年龄（或生命）阶段性状选择压力的重要性。
