The causes and consequences of intraspecific variation in standard metabolic rate

为什么个体之间生理上的巨大差异持续存在，而这似乎对生存能力有重大影响？对一个关键性状保持个体变异的一种解释是，它是非遗传起源的，是由环境或母体影响造成的，但这方面的直接证据往往很弱。该项目将调查个体之间最低代谢率差异的原因/以及后果/，通常称为基础代谢率或标准代谢率(SMR)。SMR在不同动物之间差异很大(但在内部是一致的)，并对性能有重大影响：例如，在鲑鱼中，当鱼苗是其优势地位、未来生长和存活率的重要预测指标时，个体的SMR，以及对生长效率的主要影响。然而，SMR的遗传力较低。那么，为什么SMR有如此多的表型变异？在这里，我们提出了这样的假设：不同的环境有利于不同的代谢率，代谢率是由胚胎暴露在卵子中的母体类固醇激素(睾酮和皮质醇)来编程的。以鲑鱼为研究系统，我们将通过在一系列饲养条件下对繁殖的成鱼及其后代进行实验，来检验从这一假设中产生的新预测。我们将通过荷尔蒙控制的方法来测试母鱼产卵时的荷尔蒙水平是否会影响其鱼苗的代谢率，以及来自卵巢不同部分的卵是否会收到不同水平的荷尔蒙，从而在后代体内产生代谢率(和攻击性)的变化。我们还将测试最佳代谢率(高或低)是否取决于鱼类生活的微生境，因此为这种变异的持久性提供了解释。收集到的信息将有助于了解这一基本生理特征变异的原因和后果，以及荷尔蒙作为母体工具对后代适应环境的作用，从而将内分泌学、生态生理学、行为和种群联系起来。这一结果将对当地适应和种群结构的研究，以及鱼类福利和养殖业制度的设计具有重要意义。

Why does substantial variation between individuals in their physiology persist, when it appears to have a significant effect on viability? One explanation for the maintenance of individual variation in a key trait is that it is non-genetic in origin and is created by environmental or maternal influences, but the direct evidence for this is often weak. This project will investigate the causes / and also the consequences / of variation between individuals in their minimal rate of metabolism, generally termed basal or standard metabolic rate (SMR). SMR varies considerably between (but is consistent within) individual animals and has major effects on performance: in salmonid fish, for example, an individual's SMR when a fry is a significant predictor of its dominance status, future growth and survival rate, as well as being a major influence on the efficiency of growth. However, the heritability of SMR is low. Why, then, is there so much phenotypic variation in SMR? Here we put forward the hypotheses that different environments favour different rates of metabolism, and that rates of metabolism are programmed by embryonic exposure to maternal steroid hormones (testosterone and cortisol) in the egg. Using trout as a study system, we will test novel predictions that arise from this hypothesis by means of experiments on both breeding adults and their offspring in a range of rearing conditions. We will test by means of hormone manipulations whether a mother's hormone levels at the time of spawning affect metabolic rates in her fry and whether eggs from different parts of the ovary receive different levels of hormone, so generating variation in metabolic rate (and aggression) within the offspring. We will also test whether the best metabolic rate (high or low) depends on the microhabitat in which the fish is living, so providing an explanation for the persistence of this variation. The information gathered will provide an understanding of the causes and consequences of variation in this basic physiological trait and of the role that hormones play as a maternal tool for adjusting offspring to the environment, so linking endocrinology, ecophysiology, behaviour and populations. The results will have relevance for studies of local adaptation and population structure, but also fish welfare and the design of husbandry regimes.