Ontogeny, plasticity and phenotypic evolution in the wild

当自然选择作用于具有遗传决定基础的特征时，预计进化就会发生。例如，在许多生物体中，生存和繁殖的成功取决于体型，而这一特征已知至少部分是由个体的基因组成决定的。如果我们能够测量选择的作用方式，并量化具有遗传基础的种群变异的数量，那么理论模型就可以用来预测性状将如何随着时间的推移而演变。虽然这些预测在实验室研究中很有效，但在对自然种群的研究中，结果却更加复杂。其中一个原因是，现有的理论模型并没有真正捕捉到野生系统的真正复杂性。特别是，他们倾向于忽略个体发生（或年龄）可能发生的变化，他们也假设种群处于稳定的环境中。第二个假设在人工条件下可能是合理的，但在几乎所有的自然系统中，或多或少都可能被违反。重要的是，年龄和环境的变化不仅会影响特征本身（例如，体型随着年龄的增长而增加，在更好的环境中往往更高），而且还会影响基因决定特征的方式。虽然实验工作表明，这些“基因型与环境”的相互作用很常见，但它们在自然界中很少被量化，而且人们对它们在野外决定进化过程中所起的作用知之甚少。拟议项目的主要目的是解决我们知识上的这一差距。为此，我将首先开发和扩展现有的分析模型，以便同时纳入个体发生和环境变化。其次，我将把这些模型应用于对圣基尔达群岛的苏格兰Hirta岛上的野生羊的长期研究数据。特别是，我将研究在这个系统中已知的在选择下的体型和雌性生殖策略的特征。这是一种长寿的动物种群，其特点是环境条件（气候和密度）的波动非常剧烈，因此它是研究个体发生和环境对进化影响的理想案例。通过分析性状、变异的遗传基础和自然选择的本质可能随着年龄和环境的变化而变化的方式，预计这项工作将为塑造野生生物多样性的进化过程提供深刻的见解。

Evolution is expected to occur when natural selection acts on a trait that has a genetic basis of determination. For example, in many organisms survival and reproductive success depend on body size, a trait which is known to be determined, at least in part, by an individual's genetic makeup. If we can measure the way that selection is acting and also quantify the amount of variation in the population that has a genetic basis, then theoretical models can be used to predict how the trait will evolve over time. While such predictions work well in laboratory studies, results have been more mixed in studies of natural populations. One reason for this is that existing theoretical models do not really capture the true complexities of wild systems. In particular they tend to ignore changes that may occur over ontogeny (or age), and they also assume that the population is in a stable environment. The second of these might well be a reasonable assumption under artificial conditions but is likely to be violated, to a greater of lesser extent, in almost all natural systems. Importantly, age and environmental variation can not only influence the trait itself (e.g., body size increases with age and is often higher in a better environment), but also the way in which genes act to determine the trait. While experimental work has shown that these 'genotype-by-environment' interactions are common, they have rarely been quantified in nature and very little is known about the role they play in determining evolutionary processes in the wild. The primary aim of the proposed project is to address this gap in our knowledge. To do this I will firstly develop and extend existing analytical models, in order to simultaneously incorporate ontogeny and environmental variation. Secondly I will apply these models to data from a long-term study of feral sheep on the Scottish island of Hirta in the St. Kilda archipelago. In particular, I will study the traits of body size and female reproductive strategy which are already known to be under selection in this system. This is a population of long-lived animals that is characterised by very dramatic fluctuations in environmental conditions (climate and density), and consequently it represents an ideal case-study for examining ontogenetic and environmental influences on evolution. By analysing the way in which the trait, its genetic basis of variation, and the nature of natural selection on it may all change with age and environment, it is expected that this work will provide great insights into the evolutionary processes that shape biodiversity in the wild.