MacLeod K J, Sheriff M J, Ensminger D C, Owen D A S, Langkilde T
Department of Ecosystem Science and Management, Pennsylvania State University, Forest Resources Building, University Park, PA 16802, USA; Department of Biology, Pennsylvania State University, Mueller Laboratory, University Park, PA 16802, USA; Intercollege Graduate Degree Program in Ecology, The Huck Institute of the Life Sciences, Pennsylvania State University, University Park, PA 16802, USA; Center for Brain, Behavior and Cognition, Pennsylvania State University, University Park, PA 16802, USA.
Department of Ecosystem Science and Management, Pennsylvania State University, Forest Resources Building, University Park, PA 16802, USA; Intercollege Graduate Degree Program in Ecology, The Huck Institute of the Life Sciences, Pennsylvania State University, University Park, PA 16802, USA.
Gen Comp Endocrinol. 2018 Nov 1;268:1-6. doi: 10.1016/j.ygcen.2018.07.006. Epub 2018 Aug 16.
Organisms are continuously encountering both predictable and unpredictable ecological stressors within their environment. The activation of the hypothalamic-pituitaryadrenal (stress) axis is a fundamental process allowing animals to cope with and respond to such encounters. A main consequence of HPA axis activation is the release of glucocorticoid hormones. Although short-term glucocorticoid elevations lead to changes in physiological and behavioral processes that are often adaptive, our understanding of fitness consequences of repeated acute elevations in glucocorticoid hormones over a longer time period is largely lacking. This is of particular current importance as animals are facing a significant increase in exposure to stressors including those associated with human-induced rapid environmental change. Here, we test fitness-relevant consequences of repeated exposure to glucocorticoids in the absence of natural challenges, by treating wild-caught gravid female eastern fence lizards (Sceloporus undulatus) with a daily transdermal dose of a glucocorticoid hormone until laying. This treatment causes an increase in plasma glucocorticoids that mimics the natural response lizards have when they encounter a stressor in the wild, without confounding effects associated with the encounter itself. This treatment reduced females' reproductive success (hatching success) and survival. Further, glucocorticoid-induced reductions in reproductive success were greater when females had experienced higher temperatures the previous winter. This demonstrates the potential significant consequences of repeated exposure to acute elevations in glucocorticoid hormones. Additionally, the costs of repeated glucocorticoid elevation may be further exaggerated by an individual's previous experience, such as the potential compounding effects of winter warming increasing animals' vulnerability to increased glucocorticoid levels during spring breeding.
生物体在其环境中不断面临可预测和不可预测的生态压力源。下丘脑 - 垂体 - 肾上腺（应激）轴的激活是动物应对此类遭遇并做出反应的基本过程。HPA轴激活的一个主要后果是糖皮质激素的释放。虽然短期糖皮质激素升高会导致生理和行为过程发生变化，这些变化通常具有适应性，但我们在很大程度上缺乏对较长时间内糖皮质激素反复急性升高对健康影响的了解。鉴于动物面临的压力源显著增加，包括与人为引起的快速环境变化相关的压力源，这一点在当前尤为重要。在这里，我们通过对野生捕获的怀孕雌性东部围栏蜥蜴（Sceloporus undulatus）每天经皮给予一定剂量的糖皮质激素直至产卵，来测试在没有自然挑战的情况下反复接触糖皮质激素对健康相关的影响。这种处理会使血浆糖皮质激素增加，模拟蜥蜴在野外遇到压力源时的自然反应，而不会产生与遭遇本身相关的混杂影响。这种处理降低了雌性的繁殖成功率（孵化成功率）和存活率。此外，当雌性前一个冬天经历较高温度时，糖皮质激素引起的繁殖成功率降低幅度更大。这表明反复接触糖皮质激素急性升高可能产生重大后果。此外，反复升高糖皮质激素的代价可能会因个体先前的经历而进一步加剧，例如冬季变暖的潜在复合效应会增加动物在春季繁殖期间对糖皮质激素水平升高的易感性。
