Environmental effects, thermal energetics, and avian life history variation

母亲通过胚胎发育期间的激素信号和/或通过产后护理的调整，在塑造后代的生理方面发挥着关键作用。我提出的研究的主要目标是利用野生和圈养的鸟类来了解母亲是否以一种适应性的方式为后代做好准备，以应对预测的环境变化。我和我的学生将解决三个一般性问题：(1)如果母鸟在产卵前经历了热浪，它们的雏鸟是否能更好地应对未来的高温？(2)母亲是否会调节沉积在蛋中的甲状腺激素水平，以使雏鸟为未来的温度做好准备？(3)成鸟喂养雏鸟的能力是否受到过热风险的限制？在发育过程中，母体的暗示是否会提高过热发生的温度？为了测试问题1，我们将把圈养的鸟类暴露在产卵前的模拟热浪中。然后，我们将把雏鸟饲养在与它们母亲所经历的温度“匹配”或“不匹配”的环境中。我们预测，如果母亲能够通过产前提示启动雏鸟的热生理，那么“匹配”的雏鸟将比那些经历“不匹配”温度的雏鸟生长得更快，并且能够更好地应对热浪。为了测试问题2和3，我们将学习野生树燕。我们将通过实验提高鸡蛋中的甲状腺激素水平，并在实验冷却的环境中饲养雏鸟。众所周知，甲状腺激素能提高生长速度和新陈代谢。我们预测，雏鸟暴露于甲状腺激素作为胚胎将显示较低水平的生理应激暴露在寒冷。由于母亲可能会将不同数量的激素存入蛋中，我们还将研究这是否可能是母亲调整个体雏鸟的大小等级和竞争优势的机制。为了测试问题3，我们将通过实验增加繁殖鸟类散热的能力，并使用自动无线电遥测系统测量飞行活动。我们预测，随着散热能力的增加，父母将增加他们的活动和雏鸟喂养率。为了测试饲养环境是否会改变热极限，我们将训练目标1中的鸟类在高温下运动。我们预测，母亲在产卵前经历热浪的后代将在高温下保持较高的活动，但可能会经历高活动的生理代价。总的来说，这项研究将有助于了解母亲是否能够调整后代的能力，以应对预测的温度变化，并确定可能的激素机制。这项拟议的研究将提供关键的生理数据，供研究人员和管理人员在预测种群和物种应对气候变化的能力时使用。

Mothers play a critical role in shaping the physiology of their offspring, via hormonal signals during embryonic development and/or via adjustment of postnatal care. The major goal of my proposed research is to use wild and captive birds to understand whether mothers prime their offspring in an adaptive way, to cope with predicted environmental change. My students and I will address three general questions: (1) If mothers experience heat waves prior to egg laying, are their nestlings better able to cope with high temperatures in the future? (2) Do mothers adjust levels of thyroid hormones deposited in their eggs as a mechanism to prime nestlings for future temperatures? (3) Is the ability of adult birds to feed their nestlings limited by the risk of overheating, and can the temperature at which overheating occurs be increased by maternal cues during development? To test question 1, we will expose captive birds to simulated heat waves prior to egg laying. We will then raise nestlings in environments that "match" the temperature their mother experienced or are "mismatched." We predict that if mothers can prime a nestling's thermal physiology via prenatal cues, then "matched" nestlings will have faster growth and will be better able to cope with heat waves than those that experienced "mismatched" temperatures. To test questions 2 and 3, we will study wild tree swallows. We will experimentally increase thyroid hormone levels in eggs and raise nestlings in experimentally cooled environments. Thyroid hormones are known to increase growth rates and metabolism. We predict that nestlings exposed to thyroid hormones as embryos will display lower levels of physiological stress when exposed cold. Because mothers may deposit different amounts of hormone into eggs, we will also study whether this may be a mechanism by which mothers adjust the size hierarchy and competitive advantage of individual nestlings. To test question 3, we will experimentally increase the ability of breeding birds to dissipate heat and measure flight activity using an automated radio-telemetry system. We predict that parents with an increased capacity to dissipate heat will increase their activity and nestling feeding rates. To test whether thermal limits may be modified by the rearing environment, we will train birds from Objective 1 to exercise in the heat. We predict that offspring whose mothers experienced heat waves prior to egg laying will maintain higher activity in the heat but may experience physiological costs of high activity. Overall, this research will help understand whether mothers are able to adjust the capacity of their offspring to cope with predicted temperature change and identify possible hormonal mechanisms. The proposed research will provide key physiological data that can be used by researchers and managers when predicting the capacity for populations and species to cope with climatic change.