Testing the ecological relevance of the heat dissipation limit hypothesis in a small mammal

动物在行为和生理上所做的一切都需要能量。然而，虽然有很多东西可以消耗能量，但只有一个能量/食物摄入来源。如果动物可以吃的过程和消耗无限量的能量将不会有问题，但当然他们不能，这导致导致在总可用预算内的竞争需求之间的重要权衡。能量摄入的最大速率被称为持续能量摄入或SusEI。我一直在研究SusEI的极限及其更广泛的影响，大约有10年了，最近我们在理解这些极限方面取得了重大突破。目前的建议是在这一重要进展的基础上提出的。为了将这一进展置于背景中，有必要提供一些研究领域的背景。20世纪90年代初提出了两个关于如何调解SusEI限制的想法。限制可能是由消化道和相关器官的能力（中心限制假设）或施加在能量被利用的部位（外周限制假设）。在过去的两年里，我们一直在研究一个完全不同的想法，我们的研究结果发表在去年的《实验生物学杂志》上的三篇系列论文中。我们的假设借鉴了农业观察，奶牛的性能显着影响其能力，以消散在泌乳期间产生的热量。我们在实验室小鼠中所做的观察与小鼠散热能力受到类似限制的假设/散热极限假设一致。然而，有一个问题。实验室小鼠被选择为具有异常高的后代生产力。虽然热耗散限制假说解释了我们在这个模型系统中的观察结果，但对于具有较小窝仔的野生小型哺乳动物来说，这种限制可能永远不会达到。因此，在我们能够探索这一发现的更广泛影响之前，确定我们观察结果的生态相关性至关重要。目前的建议涉及的工作将建立这一突破的生态相关性，我们的理解限制实验室小鼠的SusEI，因此可能使未来的研究范围广泛。由于SusEI的关键重要性，我们在过去已经能够利用它的研究提供了一系列重要的生态问题的重要见解。例如，了解气候变化如何影响动物分布（托马斯，Blondell和Speakman，2001年;科学;汉弗莱斯，托马斯和Speakman，2002年自然）和为什么盗寄生对非洲野狗的种群生物学有如此重要的影响（戈尔曼等人，2001年：自然）。理解限制SusEI的因素也延伸到许多其他领域，包括理解恒温动物的进化（班尼特和鲁本，1989;科学海斯和加兰，1996;生理学动物园）。以及能量平衡和肥胖的调节（例如Speakman等人2002：Proc Nut Soc）。

Everything that animals do behaviourally and physiologically requires energy. However, while there are lots of things energy can be expended on, there is only one source of that energy / food intake. If animals could eat process and expend unlimited quantities of energy there would be no problem, but of course they can't, which leads to leading to important trade-offs between competing demands within the total available budget. The maximal rate at which energy can be ingested is called the Sustained energy intake or SusEI. I have been working on the limits to SusEI and its wider ramifications for about 10 years and we have recently made a significant breakthrough in our understanding these limits. The current proposal builds on this important advance. To set this advance in context it is necessary to provide some background to the research area. Two ideas were proposed in the early 1990s concerning how limits to SusEI might be mediated. Limits might be imposed by the capacity of the alimentary tract and associated organs (the central limits hypothesis) or imposed at sites where the energy is utilised (the peripheral limits hypothesis). Over the past two years we have been working on a radically different idea, and our findings were published last year in a series of three papers in the Journal of Experimental Biology. Our hypothesis draws on agricultural observations that the performance of dairy cows is significantly affected by their capacity to dissipate heat generated during lactation. Observations we have made in laboratory mice are consistent with the hypothesis that mice similarly constrained in their capacity to dissipate heat / the heat dissipation limit hypothesis. There is, however, a problem. Laboratory mice have been selected for unusually high offspring productivity. Although the heat dissipation limitation hypothesis explains our observations in this model system, for wild small mammals, which have smaller litters, this limitation may never be reached. Establishing the ecological relevance of our observations is therefore critical before we can explore the wider ramifications of this finding. The current proposal involves work that will establish the ecological relevance of this breakthrough in our understanding of limits on SusEI of laboratory mice, therefore potentially enabling a broad spectrum of future studies. Because of the pivotal importance of SusEI, we have been able in the past to use studies of it to provide significant insights into a range of fundamentally important ecological questions. For example, understanding how climate changes influence animal distributions (Thomas, Blondell and Speakman 2001; Science; Humphries, Thomas and Speakman, 2002 Nature) and why kleptoparasitism has such an important effect on the population biology of African wild-dogs (Gorman et al 2001: Nature). The implications of understanding what limits SusEI also stretch to many other areas, including understanding the evolution of endothermy (Bennett and Ruben, 1989; Science Hayes and Garland,1996; Physiol Zool.) and the regulation of energy balance and obesity (eg Speakman et al 2002: Proc Nut Soc).