COLLABORATIVE RESEARCH: The role of glucocorticoids in mediating life history tradeoffs

所有生物体都必须将有限的资源分配给相互竞争的功能。这些功能可以分为两大类：繁衍和自我维持。繁殖可以通过繁殖后代来增加健康，而自我维持可以通过提高存活率来增加健康，使个体在未来可以繁殖。影响生殖或自我维持投资策略的一个核心因素是“生殖价值”，即当前生殖与未来生殖的相对适合性收益。我们目前还不了解动物在面对不断变化的环境条件、资源可获得性和繁殖价值时，如何自适应地分配资源用于繁殖和自我维持。糖皮质激素，或应激激素，对维持能量平衡至关重要，并可能在调节生殖分配和自我维持方面发挥重要作用。这个项目将通过对自由放养的树燕体内的糖皮质激素、生殖努力和血液寄生虫的实验操作，来测试关于糖皮质激素在调节资源分配中的作用的三个假说。这项工作的结果将提高我们对生殖和生存变异的潜在机制以及资源分配策略的演变的理解。这些信息是有价值的，因为它将提高我们对进化和生理学的理解，并将对保护关注的物种的管理产生影响。糖皮质激素水平随着栖息地的干扰而增加，因此，了解这些激素如何影响繁殖和生存可以帮助我们理解受干扰的栖息地中种群的动态。最后，由于糖皮质激素存在于包括人类在内的所有脊椎动物中，这项研究的发现可能会对人类健康产生重要影响。

All organisms must allocate limited resources towards competing functions. These functions can be grouped into two broad categories: reproduction and self-maintenance. Reproduction can increase fitness through production of offspring, whereas self-maintenance can increase fitness by improving survival to a time in the future when the individual can reproduce. One central factor influencing strategies of investment in reproduction or self-maintenance is "reproductive value", or the relative fitness benefit of current versus future reproduction. We currently do not understand the mechanisms allowing animals to adaptively allocate resources to reproduction and self-maintenance in the face of changing environmental conditions, resource availability, and reproductive value. Glucocorticoids, or stress hormones, are crucial for maintaining energetic balance, and might play an important role in mediating allocation to reproduction and self-maintenance. This project will test three hypotheses about the role of glucocorticoids in mediating resource allocation through experimental manipulations of glucocorticoids, reproductive effort, and blood parasites in free-ranging Tree Swallows. Results of this work will improve our understanding of the mechanisms underlying variation in reproduction and survival and the evolution of strategies of resource allocation. This information is valuable because it will improve our understanding of evolution and physiology, and will also have implications for management of species of conservation concern. Glucocorticoid levels increase in response to habitat disturbance, and so, an understanding of how these hormones affect reproduction and survival can inform our understanding of dynamics of populations in disturbed habitat. Finally, because glucocorticoids are found in all vertebrates, including humans, the findings from this study might have important implications for human health.