Experimental adaptation and speciation in rotifers

进化生物学试图解释自然界的两个特征：有机体对其环境的适应(适应)和不同物种的多样性。多样性取决于两个关键过程之间的平衡，即将现有物种划分为两个或更多不同的子物种(物种形成)和灭绝。在有性繁殖的生物体中，物种的定义是物种内的成功杂交以及物种之间的杂交障碍。因此，物种形成包括种群间杂交的新障碍的进化。这些障碍的进化可以通过不同的自然选择来启动，从而使一个物种内的种群适应不同的环境。为了完成物种形成过程，这种适应需要与其他成功杂交的障碍相结合，例如分类交配。理论表明，有两种主要力量反对不同的适应和物种形成的进程。这些是由于个体从一个种群迁移到另一个种群而导致的基因流动，以及重组，即打破自然选择或其他因素产生的基因组合的遗传过程。然而，由于现存物种或不同种群的复杂和未知的历史，很难在自然系统中测试这些力的影响。在这个项目中，我们将采取一种不同的方法，通过对不同选择下的种群对迁移和重组的实验控制，独立和联合地测试它们对适应和杂交障碍进化的影响。我们将在褶皱臂尾轮虫物种组中使用轮虫。这些都是小型水生动物，在实验室里很容易养殖，世代时间只有几天。它们既有有性繁殖模式，也有无性繁殖模式，这将允许我们通过改变有性模式的频率来控制重组。我们将保持无性繁殖、稀有性繁殖和频繁交配的复制对品系。在每一对中，每一条线都将受到不同的新奇、压力环境的影响，导致不同的选择。我们还将通过无连接复制、每次更新培养时一个个体在行之间移动的复制、以更高的移动速度复制和完全混合的复制来控制成对线之间的基因流动。我们将跟踪这些品系在100多个世代中的分化适应进展，并通过测量种类交配和杂交种的适合度来测试它们是否进化出其他杂交障碍。我们将对我们开始的种群和实验进化的品系的基因组进行排序。这将使我们能够确定基因流动和重组是否影响我们观察到的进化变化背后的遗传变化的数量和分布。实验进化很少被用于物种形成研究，但现在越来越多的人认识到，需要实验工作来补充自然系统的理论和分析。在这个项目中，我们将使用一个以前从未在此背景下使用过的强大的模型系统，将这种方法应用于物种形成研究的中心问题。进一步了解该项目将有助于的适应和物种形成，对于在不断变化的环境中管理生物多样性至关重要。

Evolutionary biology seeks to explain two features of the natural world: the fit of organisms to their environment (adaptation) and the diversity of different species. Diversity depends on a balance between two key processes, division of existing species into two or more distinct daughter species (speciation) and extinction. In sexually-reproducing organisms, species are defined by successful interbreeding within species combined with barriers to interbreeding between species. Thus speciation consists of the evolution of new barriers to interbreeding between populations. The evolution of these barriers can be initiated by divergent natural selection that generates adaptation of populations within a species to different environments. To complete the speciation process, this adaptation needs to be combined with other barriers to successful interbreeding such as assortative mating. Theory suggests that two major forces oppose divergent adaptation and the progression towards speciation. These are gene flow, due to the movement of individuals from one population to another, and recombination, the genetic process that breaks up combinations of genes generated by natural selection or other factors. However, it is difficult to test the effects of these forces in natural systems because of the complex and unknown history of extant species or divergent populations. In this project, we will take a different approach, using experimental control of migration and recombination in pairs of populations under divergent selection to test their effects, independently and jointly, on both adaptation and the evolution of barriers to interbreeding. We will use rotifers in the Brachionus plicatilis species group. These are small aquatic animals that are easily cultured in the laboratory with a generation time of only a few days. They have both sexual and asexual modes of reproduction and this will allow us to control recombination by varying the frequency of the sexual mode. We will maintain replicated pairs of lines without sexual reproduction, with rare sex and with frequent sex. Within each pair, each line will be subjected to a different novel, stressful environment, resulting in divergent selection. We will also control gene flow between paired lines by having replicates without connection, replicates where one individual is moved between lines each time we renew cultures, replicates with a higher rate of movement and replicates that are completely mixed. We will follow the progress of divergent adaptation in these pairs of lines over more than 100 generations and also test whether they evolve other barriers to interbreeding by measuring assortative mating and the fitness of hybrids. We will sequence the genomes of our starting populations and of the experimentally-evolved lines. This will allow us to determine whether gene flow and recombination influence the number and distribution of genetic changes underlying the evolutionary changes we observe. Experimental evolution has rarely been used in the context of speciation research but there is now an increasing recognition that experimental work is needed to complement theory and analysis of natural systems. With this project, we will apply this approach to central issues in speciation research using a powerful model system that has not previously been used in this context. The further understanding of adaptation and speciation to which this project will contribute is critical for the management of biological diversity in a changing environment.