Lynn Sharon E, Kern Michael D, Fitzgerald Kimberly, Will Alexis, Kitaysky Alexander
The College of Wooster, Department of Biology, 931 College Mall, Wooster, OH 44691, USA.
The College of Wooster, Department of Biology, 931 College Mall, Wooster, OH 44691, USA.
Gen Comp Endocrinol. 2022 May 1;320:114001. doi: 10.1016/j.ygcen.2022.114001. Epub 2022 Feb 17.
Exposure to noxious stimuli early in life can both activate and shape the development of the hypothalamic-pituitary-adrenal (HPA) axis in birds and other vertebrates, with the potential for lifelong consequences. Studies assessing early HPA axis activation often rely on collection of blood samples to evaluate circulating glucocorticoid levels. However, blood sampling in small altricial young is invasive, limited by animal size, and not sufficient to provide detailed information about hormone exposure over protracted periods of time. We tested the use of feather corticosterone as an alternative method to assess HPA axis activity early in life in free-living, altricial chicks, for whom timing of growth of first feathers coincides with a period of rapid growth, development of the HPA axis, and reliance on parental care. We investigated (1) whether ecologically relevant bouts of experimental cooling prior to the onset of homeothermy-conditions known to elevate circulating corticosterone-are reflected in changes of feather corticosterone deposition in Eastern bluebird (Sialia sialis) chicks, and (2) whether such changes occurred in a sex-dependent manner. We found that cooling during the first week of life resulted in elevated feather corticosterone in first-grown feathers of experimentally cooled chicks relative to controls. The timing of deposition of corticosterone in feathers in response to temperature treatments was delayed in females compared to males. Results indicate that the hormone deposition in feather tissues of altricial nestlings reflects exposure to environmental stimuli, and can thus provide a minimally invasive tool for assessing HPA activity in early life. The development of the HPA axis, or its activation in response to environmental stimuli early in life, may also occur in a sex-dependent manner in altricial birds.
生命早期接触有害刺激会激活并塑造鸟类和其他脊椎动物下丘脑-垂体-肾上腺（HPA）轴的发育，可能产生终身影响。评估早期HPA轴激活的研究通常依赖采集血样来评估循环糖皮质激素水平。然而，对小型晚成雏进行采血具有侵入性，受动物体型限制，且不足以提供有关长时间激素暴露的详细信息。我们测试了使用羽毛皮质酮作为一种替代方法，来评估自由生活的晚成雏鸟生命早期的HPA轴活动，对于这些雏鸟而言，第一根羽毛的生长时间与快速生长、HPA轴发育以及对亲代照料的依赖期相吻合。我们研究了：（1）在恒温开始前进行的与生态相关的实验性降温——已知这种情况会升高循环皮质酮——是否会反映在东部蓝鸲（Sialia sialis）雏鸟羽毛皮质酮沉积的变化中；（2）这种变化是否存在性别差异。我们发现，在出生后第一周进行降温处理，与对照组相比，实验性降温雏鸟首次生长的羽毛中羽毛皮质酮升高。与雄性相比，雌性对温度处理作出反应时皮质酮在羽毛中的沉积时间延迟。结果表明，晚成雏鸟巢中雏鸟羽毛组织中的激素沉积反映了对环境刺激的暴露，因此可以提供一种微创工具来评估生命早期的HPA活性。在晚成雏鸟类中，HPA轴的发育或其在生命早期对环境刺激的激活也可能存在性别差异。
