The genetics of competition: does resource limitation constrain evolution?

当资源(例如，食物、配偶、空间)有限时，动物之间就会发生竞争。尽管它们对生长和繁殖的影响长期以来一直是种群生物学家感兴趣的，但竞争性相互作用也可能对我们理解进化是如何工作的具有深远的、但在很大程度上没有被认识到的影响。这是因为，虽然我们通常认为竞争是由纯粹的环境影响(例如，缺乏食物)引起的，但竞争的结果(即，哪种动物‘获胜’)可能关键取决于基因。这给生物学家带来了问题，打破了遗传和环境影响的传统分离，这是大多数进化论研究的起点。竞争可以被认为是一种环境效应，但我们需要承认，竞争本身就有发展的潜力。这种可能性通常不会被支持进化论研究的理论所解释，实际上可能会对许多纯理论和应用研究领域产生巨大影响--从生态学和动物行为，到家畜饲养和促进动物福利。例如，想象一个基因通过对觅食的影响来影响动物的生长--这种基因的某些版本(称为‘等位基因’)使个体比普通的觅食者更好，因此可能生长得更快。我们可能会认为，选择携带这些等位基因的个体将导致更快的生长进化。然而，如果食物是有限的，那么通过允许一个人主宰对资源的获取来促进一个人的生长的基因，实际上会导致其他人吃得更少，从而生长得更慢。从这个角度来看，选择成长更快的个体将带来一个更具竞争力的环境，这将抵消(甚至可能逆转)我们最初对增长率将会增加的预期。这种类型的过程可能会对性状对选择的反应程度施加限制，要么是野生动物种群中发生的自然选择，要么是动物育种者强加的人工选择。此外，由于竞争往往涉及攻击性行为(例如，动物为有限的资源而打架)，任何无意中导致更具竞争性的环境的选择也可能损害动物的福利。因此，尽管竞争显然会对资源依赖型特征的进化产生巨大影响，但我们目前几乎没有关于这些影响实际上有多广泛或多大的信息。虽然方法学上的限制限制了迄今为止的进展，但最近开发的一些统计方法意味着这些问题现在可以得到解决。因此，我建议对竞争的遗传学进行一次全面的调查，评估它在形成和限制生长和其他资源受限特征的进化中所起的作用。要做到这一点，我将采取两种方法。首先，我将对实验室中的一群鱼(即绿剑尾鱼)进行一系列实验。这将使我能够直接操纵关键变量，如食物可获得性、竞争个体的数量以及竞争对手之间的关系，从而检验源于理论预测的几个假设。其次，我将应用新的统计方法来测试两个商业牲畜种群(大西洋鲑鱼和鸡)竞争能力的遗传变异。使用这两个高质量的数据集将补充实验工作，并允许直接评估这一研究方向的应用潜力。

Competition occurs among animals when resources (e.g., food, mates, space) are limited. Although their impacts on growth and reproduction have long interested population biologists, competitive interactions may also have profound, but largely unrecognised, implications for our understanding of how evolution works. This is because while we normally think of competition as arising from purely environmental effects (e.g. lack of food), its outcome (i.e., which animal 'wins') may depend critically on genes. This causes problems for biologists by breaking down the traditional separation of genetic and environmental effects which is the starting point for most studies of evolution. Competition can be thought of as an environmental effect, but we need to acknowledge that it is one with the potential to evolve in its own right. This possibility is not usually accounted for by the theory underpinning evolutionary studies, and may actually have enormous consequences for many fields of pure and applied research - from ecology and animal behaviour, to livestock breeding and the promotion of animal welfare. For example, imagine a gene that influences an animal's growth through effects on foraging - with some versions of the gene (termed 'alleles') making individuals better than average foragers, and therefore likely to grow faster. We might expect that selection of individuals carrying these alleles would result in evolution of faster growth. However, if food is limited, then a gene that increases one individual's growth by allowing it to dominate access to a resource, would actually cause other individuals to get less to eat, and therefore grow more slowly. Seen from this point of view, selection of faster growing individuals would lead to a more competitive environment which would act to counter (and possibly even reverse) our initial expectation that growth rate will increase. This type of process could impose limits on the extent to which traits respond to selection, either natural selection occurring in a wild animal population, or artificial selection being imposed by an animal breeder. Additionally, since competition often involves aggressive behaviours (e.g., animals fighting over a limited resource), any selection that inadvertently leads to a more competitive environment may also be detrimental to animal welfare. Although it is therefore clear that competition could have enormous implications for the evolution of resource-dependent traits, we currently have very little information about how widespread or large these effects actually are. While methodological limitations have restricted progress to date, a number of recently developed statistical approaches mean that these questions can now be addressed. I therefore propose to conduct a comprehensive investigation of the genetics of competition, assessing the role that it plays in shaping, and constraining the evolution of growth and other resource-limited traits. To do this I will take two approaches. Firstly I will perform a series of experiments on a laboratory population of fish (namely the green swordtail, Xiphophorus helleri). This will allow me to directly manipulate key variables such as food availability, the number of competing individuals, and relationships among competitors thereby testing several hypotheses that stem from theoretical predictions. Secondly, I will apply novel statistical methods to test for genetic variation in competitive ability in two commercial livestock populations (Atlantic salmon, chickens). Use of these two high quality data sets will complement the experimental work, and also allow a direct assessment of the applied potential for this direction of research.