Schoenle Laura A, Zimmer Cedric, Vitousek Maren N
Department of Global Health, University of South Florida, Tampa, FL 33620, USA.
Department of Biology, Hamilton College, Clinton, NY 13323, USA.
Integr Comp Biol. 2018 Oct 1;58(4):777-789. doi: 10.1093/icb/icy046.
It has been well-established that there is variation in the strength and direction of the relationship between circulating glucocorticoids (GCs) and fitness. When studies demonstrate such variation or the direction of the GC-fitness relationship is unexpected, the results are often attributed to context-dependency. However, descriptors of context can be vague (e.g., "environmental context") and few studies explicitly test how the optimal hypothalamic-pituitary-adrenal (HPA) axis response to stressors varies across specific contexts. Although existing hypotheses create a strong foundation for understanding GC-fitness relationships, many do not provide explicit predictions of how, when, and why the relationships will change. Here, we discuss three broad factors which we expect to shape the relationships between HPA axis activity and fitness metrics: (1) whether the HPA axis-mediated response matches the challenge, (2) the intensity and frequency of challenges, and (3) life history. We also make predictions for how these factors might affect GC-fitness relationships and discuss ways to test these predictions. Observational studies, experimental manipulations of context, and large-scale cross-species comparisons will be critical to understanding the observed variation in GC-fitness relationships.
循环糖皮质激素（GCs）与健康状况之间关系的强度和方向存在差异，这一点已经得到充分证实。当研究表明存在这种差异，或者GC-健康状况关系的方向出乎意料时，结果通常归因于情境依赖性。然而，情境的描述可能很模糊（例如，“环境情境”），而且很少有研究明确测试下丘脑-垂体-肾上腺（HPA）轴对应激源的最佳反应如何在特定情境中变化。尽管现有假说是理解GC-健康状况关系的坚实基础，但许多假说并未明确预测这些关系将如何、何时以及为何发生变化。在这里，我们讨论我们预期会塑造HPA轴活动与健康指标之间关系的三个广泛因素：（1）HPA轴介导的反应是否与挑战相匹配，（2）挑战的强度和频率，以及（3）生活史。我们还预测了这些因素可能如何影响GC-健康状况关系，并讨论了检验这些预测的方法。观察性研究、情境的实验操纵以及大规模跨物种比较对于理解GC-健康状况关系中观察到的差异至关重要。
