Integration of Water and Energy Balance in Hummingbirds

[9514351] Beuchat蜂鸟是脊椎动物中新陈代谢率最高的，它们几乎完全依靠花蜜中的糖来促进这种巨大的新陈代谢。维持高代谢率的流食给这些鸟类带来了一些特殊的生理问题。最明显的是，蜂鸟必须消耗大量的花蜜，每天消耗的花蜜是其自身体重的五倍！然后，当花蜜快速通过鸟类时，胃肠道必须能够高效地提取花蜜中的糖和其他营养物质。肾脏还必须能够过滤和排泄多余的水分，以避免体液的稀释。最后，因为花蜜中盐和矿物质的浓度通常很低，但却是鸟类所需要的，所以通过尿液排出的量必须是最少的。这项研究调查了蜂鸟同时应对这些极端生理挑战的方式，包括液体、电解质和能量平衡。本研究的重点不仅是了解蜂鸟肾脏和肠道生理的基本方面，而且还研究了这些器官系统如何在能量和渗透稳态的生理维持中发挥协调作用。通过考虑肾脏和肠道功能与蜂鸟生物学在有机体水平上的整合，在一系列问题中进一步扩展了这项工作，这些问题涉及生理学与行为、形态学、生态学和进化的接口。比较生理学对我们理解陆生鸟类和哺乳动物的渗透调节的贡献很大程度上是基于对终极集中者——沙漠啮齿动物和少数几种鸟类的研究。相比之下，我们对鸟类和哺乳动物面临的特殊渗透调节问题所知相对较少，它们面临的挑战是过量的水而不是干燥。这项研究在其视角的广度和同时考虑从细胞水平到该领域动物的过程方面是不寻常的。这是第一次仔细研究鸟类或哺乳动物的渗透调节生理学，它们是脊椎动物利尿研究的模式生物。

9514351 Beuchat Hummingbirds have the highest metabolic rate of any vertebrate, and they fuel this tremendous metabolism almost entirely with the sugar found in nectar. Supporting a high metabolic rate on liquid diet presents these birds with some special physiological problems. Most obviously, hummingbirds must consume tremendous quantities of nectar, up to five times the bird's own body mass per day! Then, the gastrointestinal tract must be able to extract, with great efficiency, the sugar and other nutrients in the nectar as it passes rapidly through the bird. The kidney must also be able to filter and excrete excess water to avoid dilution of body fluids. Finally, because concentrations of salts and minerals in nectar are typically low but are needed by the bird, the amounts excreted in the urine must be minimal. This research investigates the ways in which hummingbirds deal simultaneously with these extreme physiological challenges of fluid, electrolyte, and energy balance. The study focuses not only on understanding fundamental aspects of the physiology of the kidney and intestinal tract in hummingbirds, but also on how these organ systems play coordinated roles in the physiological maintenance of energy and osmotic homeostasis. The work is further extended by considering the integration of renal and intestinal function with hummingbird biology at the organismal level in a series of questions that address the interface of physiology with behavior, morphology, and ecology, and evolution. Much of what comparative physiology has contributed to our understanding of osmoregulation in terrestrial birds and mammals has been based upon studies of the ultimate concentrators, the desert rodents, and only a few species of birds. We know relatively little, by contrast, about the special osmoregulatory problems faced by birds and mammals for which the challenge is an exc ess of water rather than desiccation. This study is unusual in the breadth of its perspective and its simultaneous consideration of processes from the cellular level to that of the animal in the field. It is the first study to closely examine the osmoregulatory physiology of a bird or mammal that is a model organism for the study of diuresis in vertebrates.