Florida State University Department of Biological Science, 319 Stadium Dr., Tallahassee, FL 32306-4295, United States; Bennington College, Science and Mathematics, 1 College Dr., Bennington, VT 05201, United States.
Florida State University Department of Biological Science, 319 Stadium Dr., Tallahassee, FL 32306-4295, United States.
Gen Comp Endocrinol. 2021 Jan 1;300:113639. doi: 10.1016/j.ygcen.2020.113639. Epub 2020 Oct 2.
When vertebrates are exposed to stressors, the subsequent acute increase in glucocorticoids by the hypothalamic-pituitaryadrenal (HPA) axis triggers a suite of adaptive responses, including mobilization of stored energy and repression of non-essential processes. However, chronic exposure to high concentrations of glucocorticoids can lead to metabolic dysregulation, impaired immune function, and cognitive decline. In developing young, this hormonal stress response shows considerable variation. Generally, the physiological stress response of young of precocial species is comparable to that of adults, whereas offspring of altricial species exhibit an attenuated response compared to adults. The developmental hypothesis of the HPA axis proposes that the dampened stress response in dependent offspring is an adaptive response to avoid the negative effects of elevated glucocorticoids, particularly in altricial species where young lack the ability to mitigate stressful stimuli.We aimed to test the developmental hypothesis in a tropical avian species, the lance-tailed manakin (Chiroxiphia lanceolata). We predicted that nestlings of this altricial species should have a dampened corticosterone response, in both magnitude and duration, compared to that of adults. We also predicted that recently fledged hatch-year birds would display a response intermediate to that of adults and nestlings. We quantified circulating corticosterone levels in adults, recently fledged hatch-year birds, and 11-day-old nestlings using a standardized capture and restraint protocol. Nestlings showed a lower maximal corticosterone response and faster negative feedback compared to adults. Further, five post-fledging hatch-year birds showed a feedback response intermediate to those of nestlings and adults. However, we caution against generalizing about fledgling responses beyond this study due to the small sample (n = 5). Interestingly, lance-tailed manakin nestlings appear to return to baseline concentrations faster than nestlings of temperate species. These results support the developmental hypothesis of the HPA axis explaining variation in stress response. This study is the first to assess the development of the hormonal stress response in nestlings of a tropical bird, which is of interest because of our still-developing understanding of how tropical and temperate species differ physiologically. Finally, findings here underscore the importance of validating and adjusting sampling protocols that quantify nestling stress responses, as sampling timelines identified for adults may underestimate the magnitude of the nestling stress response.
当脊椎动物暴露于应激源时，下丘脑-垂体-肾上腺 (HPA) 轴随后急性增加的糖皮质激素会引发一系列适应性反应，包括动员储存的能量和抑制非必需过程。然而，长期暴露于高浓度的糖皮质激素会导致代谢失调、免疫功能受损和认知能力下降。在发育中的幼体中，这种激素应激反应表现出相当大的差异。一般来说，早熟物种幼体的生理应激反应与成体相当，而晚熟物种的幼体与成体相比表现出较弱的反应。HPA 轴的发育假说提出，依赖后代的应激反应减弱是一种适应性反应，以避免升高的糖皮质激素的负面影响，特别是在晚熟物种中，幼体缺乏减轻应激刺激的能力。我们旨在在一种热带鸟类，长尾阔嘴鸟（Chiroxiphia lanceolata）中测试 HPA 轴的发育假说。我们预测，这种晚熟物种的雏鸟在幅度和持续时间上的皮质酮反应都应该减弱，与成体相比。我们还预测，最近刚离巢的雏鸟的反应将介于成体和雏鸟之间。我们使用标准化的捕获和约束方案来量化成体、最近离巢的雏鸟和 11 天大的雏鸟的循环皮质酮水平。与成体相比，雏鸟的最大皮质酮反应较低，负反馈较快。此外，5 只离巢的雏鸟的反馈反应介于雏鸟和成体之间。然而，由于样本量小（n=5），我们警告不要将离巢幼鸟的反应推广到本研究之外。有趣的是，长尾阔嘴鸟的雏鸟似乎比温带物种的雏鸟更快地恢复到基线浓度。这些结果支持 HPA 轴的发育假说，该假说解释了应激反应的变化。这是首次评估热带鸟类雏鸟的激素应激反应的发育，这是因为我们对热带和温带物种在生理上的差异的理解仍在发展。最后，本研究强调了验证和调整量化雏鸟应激反应的采样方案的重要性，因为为成体确定的采样时间线可能低估了雏鸟应激反应的幅度。
