Experimental adaptation and speciation in rotifers

进化生物学试图解释自然界的两个特征：生物体对环境的适应（适应性）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，即现存物种分裂为两个或更多不同的子种（物种形成）和灭绝。在有性繁殖的生物体中，物种是通过物种内成功的杂交以及物种间杂交的障碍来定义的。因此，物种形成包括种群间杂交的新障碍的进化。这些障碍的进化可能是由不同的自然选择引起的，这种自然选择使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阻碍杂交成功的障碍结合起来，比如同型交配。理论表明，有两股主要力量反对分化适应和向物种形成发展。基因流动是指个体从一个种群迁移到另一个种群；重组是指由自然选择或其他因素产生的基因组合被破坏的遗传过程。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量的影响。在这个项目中，我们将采取一种不同的方法，在不同的选择下对成对的种群进行迁移和重组的实验控制，以测试它们对适应和杂交障碍进化的影响，无论是独立的还是共同的。我们将在臂轮虫种类组中使用轮虫。这些小型水生动物很容易在实验室培养，一代时间只有几天。它们既有有性繁殖模式，也有无性繁殖模式，这将使我们能够通过改变有性繁殖模式的频率来控制重组。我们将保持无性繁殖、罕见性繁殖和频繁性繁殖的复制对。在每一对中，每一条线都将受到不同的新奇的、有压力的环境，从而导致不同的选择。我们还将通过不连接的复制来控制成对系之间的基因流动，每次更新培养物时都有一个个体在不同的系之间移动的复制，以更高的移动率复制和完全混合的复制。我们将在超过100代的时间里跟踪这些对系的分化适应的进展，并通过测量分类交配和杂交种的适应性来测试它们是否进化出了其他的杂交障碍。我们将对我们的起始种群和实验进化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了我们观察到的进化变化背后的遗传变化的数量和分布。实验进化很少在物种形成研究的背景下使用，但现在越来越多的人认识到实验工作需要补充自然系统的理论和分析。在这个项目中，我们将使用一个强大的模型系统将这种方法应用于物种形成研究的核心问题，而这个模型系统以前从未在此背景下使用过。该项目将有助于进一步了解适应和物种形成，这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.