Data from: Experimental effects of early-life corticosterone on the HPA axis and pre-migratory behaviour in a wild songbird

1.Although laboratory studies have shown that chronic exposure to elevated glucocorticoids during development can have profound effects on the physiology and behaviour of animals, we still have a poor understanding of the proximate and ultimate consequences of early-life stress on individuals in the wild. 2. In an island population of Savannah sparrows (Passerculus sandwichensis), we examined multiple hypotheses to explain how elevated glucocorticoid exposure during the nestling period influenced both hypothalamic-pituitary-adrenal (HPA) axis function during the nestling period and the subsequent movement and survival of young after they fledged the nest. 3. We exposed nestlings to exogenous corticosterone from 2-6 d of age and then measured both baseline and stress-induced (30 min restraint) plasma corticosterone levels prior to fledging (d 7). We then recaptured young throughout the pre-migratory period and used mark-recapture analysis to estimate temporary emigration from the capture site (movement) and survival. 4. Corticosterone-treated nestlings had higher baseline corticosterone levels and lower stress reactivity than untreated individuals, and were more sensitive to inclement weather. Although there was no evidence that corticosterone treatments influenced survival, treated individuals had higher rates of temporary emigration outside of the study site than sham or controls. 5. Our results provide support for the ceiling hypothesis, which suggests that individuals with chronic elevated glucocorticoids can lead to a dampened HPA axis response. We also provide support for the CORT-activity hypothesis, which suggests that elevated glucocorticoids can increase activity levels, at least 1-2 months after leaving the nest. Our study highlights the importance of tracking individuals across multiple stages of the annual cycle to understand how early life events carry-over to influence both physiology and behaviour.1. 尽管已有实验室研究证实，动物在发育阶段长期暴露于升高的糖皮质激素(Glucocorticoids)，会对其生理与行为产生深远影响，但我们对野生个体早期生活压力的近因与终极后果仍缺乏深入认知。 2. 本研究以一座岛屿上的萨凡纳带鹀(Savannah sparrows, Passerculus sandwichensis)种群为研究对象，通过验证多项假说，旨在阐明雏鸟期糖皮质激素暴露水平升高，如何同时影响雏鸟阶段的下丘脑-垂体-肾上腺(Hypothalamic-pituitary-adrenal, HPA)轴功能，以及幼鸟离巢后的扩散与存活情况。 3. 研究人员于雏鸟2至6日龄时为其施加外源性皮质酮(Exogenous Corticosterone)处理，并在雏鸟离巢前（第7日）分别测定其基础血浆皮质酮水平与应激诱导（30分钟束缚处理）后的血浆皮质酮水平。随后在预迁徙阶段全程对幼鸟进行重捕，借助标记重捕法(Mark-recapture Analysis)估算研究样地内个体的临时迁出率（即扩散水平）与存活率。 4. 经皮质酮处理的雏鸟，其基础皮质酮水平高于未处理个体，应激反应性则更低，且对恶劣天气更为敏感。尽管未发现皮质酮处理对存活率存在显著影响，但处理组个体临时迁出研究样地的比例显著高于假处理组(Sham Group)与对照组(Control Group)。 5. 本研究结果支持上限假说(Ceiling Hypothesis)，即长期糖皮质激素水平升高的个体，其HPA轴应激反应会被抑制；同时也支持皮质酮-活动假说(CORT-Activity Hypothesis)，即糖皮质激素水平升高可提升个体活动水平，该效应至少在离巢后的1至2个月内依然存在。本研究强调，需在年度生活周期的多个阶段对个体进行追踪，方能阐明早期生活事件如何通过遗留效应影响动物的生理与行为。