Newman Amy E M, Hess Helmi, Woodworth Bradley K, Norris D Ryan
Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
Department of Integrative Biology, University of Guelph, Guelph, ON N1G 2W1, Canada.
Gen Comp Endocrinol. 2017 Sep 1;250:80-84. doi: 10.1016/j.ygcen.2017.05.022. Epub 2017 May 31.
The hypothalamic-pituitary-adrenal (HPA) axis has been studied extensively in adults, but the HPA axis in early life is not well characterized, and there is an immense amount of unexplained variation in glucocorticoid levels during early life, especially in wild animals. To characterize population-wide natural variation in early-life HPA axis function, we compared plasma corticosterone levels (at baseline and after 30min acute restraint-stress) from seven-day-old nestlings (n=123) from a free-living, marked population of Savannah sparrows (Passerculus sandwichensis). We found a surprising sensitivity of the HPA axis to timing of sample collection across time scales. Even within the accepted 3-min framework to collect baseline samples, time to collect blood had a significant effect on baseline corticosterone concentrations. Daily rhythms also influenced baseline levels, which increased significantly during the relatively short window of sample collection (1100 and 1600). On a broader timeframe, there was a strong effect of hatch date (over a 2month period) on HPA axis responsiveness, where nestlings hatched later in the breeding season had lower stress-induced corticosterone levels than those hatched earlier. The ecophysiological mechanisms and implications of these patterns warrant future investigation; meanwhile this study highlights the critical need to consider, and potentially restrict, time across scales when collecting blood samples from wild birds to assess stress physiology.
下丘脑-垂体-肾上腺（HPA）轴在成年人中已得到广泛研究，但早期生命阶段的HPA轴特征尚不明确，而且在生命早期，尤其是野生动物的糖皮质激素水平存在大量无法解释的变异。为了描述全种群早期生命阶段HPA轴功能的自然变异，我们比较了来自自由生活、有标记的萨凡纳麻雀（Passerculus sandwichensis）种群的7日龄雏鸟（n = 123）的血浆皮质酮水平（基线时和急性约束应激30分钟后）。我们发现HPA轴在不同时间尺度上对样本采集时间具有惊人的敏感性。即使在公认的3分钟基线样本采集框架内，采血时间对基线皮质酮浓度也有显著影响。每日节律也影响基线水平，在相对较短的样本采集窗口（1100和1600）内显著升高。在更广泛的时间范围内，孵化日期（超过2个月）对HPA轴反应性有强烈影响，繁殖季节后期孵化的雏鸟应激诱导的皮质酮水平低于早期孵化的雏鸟。这些模式的生态生理机制及其影响值得未来进行研究；与此同时，本研究强调了在从野生鸟类采集血样以评估应激生理学特征时，跨尺度考虑并可能限制采样时间的迫切需求。
