Institute of Evolutionary Biology, University of Edinburgh West Mains Road, Edinburgh, EH9 3JT, U.K.
CCMar, University of Algarve Campus de Gambelas, 8005-139, Faro, Portugal.
Ecol Evol. 2015 Feb;5(3):618-33. doi: 10.1002/ece3.1395. Epub 2015 Jan 11.
It is widely expected that physiological and behavioral stress responses will be integrated within divergent stress-coping styles (SCS) and that these may represent opposite ends of a continuously varying reactive-proactive axis. If such a model is valid, then stress response traits should be repeatable and physiological and behavioral responses should also change in an integrated manner along a major axis of among-individual variation. While there is some evidence of association between endocrine and behavioral stress response traits, few studies incorporate repeated observations of both. To test this model, we use a multivariate, repeated measures approach in a captive-bred population of Xiphophorus birchmanni. We quantify among-individual variation in behavioral stress response to an open field trial (OFT) with simulated predator attack (SPA) and measure waterborne steroid hormone levels (cortisol, 11-ketotestosterone) before and after exposure. Under the mild stress stimulus (OFT), (multivariate) behavioral variation among individuals was consistent with a strong axis of personality (shy-bold) or coping style (reactive-proactive) variation. However, behavioral responses to a moderate stressor (SPA) were less repeatable, and robust statistical support for repeatable endocrine state over the full sampling period was limited to 11-ketotestosterone. Although post hoc analysis suggested cortisol expression was repeatable over short time periods, qualitative relationships between behavior and glucocorticoid levels were counter to our a priori expectations. Thus, while our results clearly show among-individual differences in behavioral and endocrine traits associated with stress response, the correlation structure between these is not consistent with a simple proactive-reactive axis of integrated stress-coping style. Additionally, the low repeatability of cortisol suggests caution is warranted if single observations (or indeed repeat measures over short sampling periods) of glucocorticoid traits are used in ecological or evolutionary studies focussed at the individual level.
人们普遍预期，生理和行为应激反应将在不同的应激应对方式（SCS）中整合，而这些方式可能代表着一个连续变化的反应性-主动性轴的两个极端。如果这种模式是有效的，那么应激反应特征应该是可重复的，生理和行为反应也应该沿着个体间变异的主要轴以综合的方式发生变化。虽然有一些证据表明内分泌和行为应激反应特征之间存在关联，但很少有研究同时包含这两种特征的重复观察。为了验证这个模型，我们在一个人工饲养的 Xiphophorus birchmanni 种群中使用了一种多变量、重复测量的方法。我们量化了个体在经历模拟捕食者攻击的野外试验（OFT）时的行为应激反应的个体间差异，并在暴露前后测量了水中的类固醇激素水平（皮质醇、11-酮睾酮）。在轻度应激刺激（OFT）下，个体间的（多变量）行为变化与强烈的个性（害羞-大胆）或应对方式（反应性-主动性）变化一致。然而，对中度应激源（SPA）的行为反应则不太可重复，并且在整个采样期间，对可重复的内分泌状态的强有力的统计支持仅限于 11-酮睾酮。尽管事后分析表明皮质醇表达在短时间内是可重复的，但行为和糖皮质激素水平之间的定性关系与我们的先验预期相反。因此，虽然我们的结果清楚地显示了与应激反应相关的行为和内分泌特征的个体间差异，但这些特征之间的相关结构与简单的主动-被动综合应激应对方式轴不一致。此外，皮质醇的低可重复性表明，如果在以个体为基础的生态或进化研究中使用糖皮质激素特征的单次观察（或实际上是短时间采样期间的重复测量），则需要谨慎。
