Lean mass dynamics during flight and refueling in migratory birds: causes, consequences, and mechanisms

候鸟完成繁殖地和越冬地之间的长途旅行。这一旅程由一系列长途直达飞行组成，对大多数鸣禽来说，持续时间可达6-8小时，但对一些滨鸟来说，可能会持续数天。在飞行期间，代谢率非常高，候鸟主要用储存的脂肪为这些长途飞行提供燃料。然而，在飞行过程中也会发生蛋白质分解，导致器官和肌肉质量急剧减少。肌肉和器官质量的急剧减少可能会导致器官系统的重大功能损失，但这还没有得到彻底的调查。该项目旨在研究候鸟飞行过程中蛋白质分解的原因、后果和机制。这项研究将进一步加深我们对候鸟在飞行中的独特新陈代谢的认识，加深我们对候鸟如何在关键器官系统急剧减少的情况下保持体内平衡的理解，并将为参与肌肉和器官退化和再生的分子和生化机制提供新的见解。此外，该项目将提供一个平台，让来自不同背景的许多本科生和研究生参与综合研究，提供适用于许多STEM领域的广泛尖端技术的接触和培训。这些学生还将为当地低收入学区的中学生开发和实施科学交流和推广计划。飞行期间，新陈代谢速度比休息时高10倍，失水率非常高，对鸟类管理水和能源收支的能力提出了极高的要求。候鸟主要通过脂肪的氧化为长时间飞行提供动力，但大量的蛋白质也被分解代谢，导致肌肉和器官质量比飞行前减少20%-40%。然而，飞行过程中瘦体重分解代谢的功能极限和潜在机制仍不清楚。候鸟将在气候控制的风洞中长时间飞行，以评估蛋白质分解代谢原因的假说，而蛋白质分解代谢的后果和机制将通过测量关键生理过程中整个动物和组织水平的变化，以及通过调查飞行过程中发生的转录差异来评估。这将使我们深入了解在器官和肌肉发生剧烈重构的情况下维持内稳态的生理机制，并将进一步了解控制脊椎动物表型灵活性的基本机制。作为该项目的一部分，研究生和本科生将接受许多尖端技术的综合培训，该项目将广泛适用于许多STEM职业。这项研究将为许多本科生提供真正的研究经验，重点是提供指导和培训，以鼓励来自代表性不足群体的妇女和学生在STEM学科进一步追求职业生涯。

Migratory birds complete long journeys between the breeding and wintering grounds. This journey is comprised of a series of long-distance non-stop flights that can be 6-8 hours in duration for most songbirds, but could last for days in some shorebirds. During flight, metabolic rate is very high and migratory birds primarily fuel these long flights with stored fat. However, protein breakdown also occurs during flight resulting in dramatic organ and muscle mass reductions. Such dramatic reductions in muscle and organ mass could result in significant functional losses of organ systems but this has not been thoroughly investigated. This project proposes to investigate the causes, consequences, and mechanisms of protein breakdown during flight in migratory birds. This research will further our insight into the unique metabolism of migratory birds in flight, deepen our understanding of how migratory birds maintain homeostasis despite dramatic reductions in critical organ systems, and will provide novel insight into the molecular and biochemical mechanisms involved in muscle and organ degeneration and regeneration. Additionally, this project will provide a platform to engage many undergraduate and graduate students from diverse backgrounds in integrative research, providing exposure and training in a broad range of cutting edge techniques that will be applicable to many STEM fields. These students will also develop and implement science communication and outreach programming for middle school students in a local low-income school district.During flight, metabolic rate is 10-fold higher than at rest and rates of water loss are very high, placing extreme demands on the ability of birds to manage water and energy budgets. Migratory birds fuel long-duration flight primarily by the oxidation of fat, but a large amount of protein is also catabolized, resulting in reductions in muscle and organ mass of 20% - 40% from pre-flight levels. However, the functional limits and underlying mechanisms of lean mass catabolism during flight remain unclear. Migratory birds will be flown in a climatically controlled wind tunnel for extended periods to evaluate hypotheses for the causes of protein catabolism, while the consequences and mechanisms of protein catabolism will be assessed by measuring whole animal and tissue level changes in key physiological processes, and by investigating transcriptional differences that occur during flight. This will provide insight into physiological mechanisms that allow the maintenance of homeostasis despite dramatic organ and muscle remodeling, and will further our understanding of the basic mechanisms controlling phenotypic flexibility in vertebrates. Graduate and undergraduate students will receive integrative training in many cutting-edge techniques as part of this project, which will be broadly applicable to many STEM careers. This research will provide genuine research experiences for many undergraduates with emphasis on providing mentorship and training to encourage women and students from underrepresented groups to further pursue careers in STEM disciplines.