The evolutionary causes and consequences of sex and sexual dimorphism

有性生殖很普遍，在大多数动物和一些植物中，有性生殖涉及两性。该研究计划的长期目标是了解有性生殖的进化原因和后果，特别是在两性系统中。一个中心目标是量化性别选择，并了解这种选择产生的各种机制。第二个目标是了解两种不同性别进化的后果。其中一组项目关注的是一种既能有性繁殖又能无性繁殖的植物，即地茅（Marchantia polymorpha）。我们将研究来自北美不同地区的这种物种的种群基因组学，以推断种群在性繁殖的频率上是否存在差异。如果是这样，那么我们就可以推断，是否像预测的那样，更高的性比率对选择的有效性产生了积极的影响。第二组项目旨在了解性别选择，这是进化生物学的一大未知。成熟的理论表明，性别选择应该通过性别如何影响适合度的平均值或方差来进行，但几乎没有数据评估自然界中这些影响。在实地研究中，我们将测量实验产生的有性和无性衍生后代的适合度分布。额外的实验将集中于测试选择的关键生态来源。第二组项目侧重于男性和女性之间的差异。选择往往倾向于两性的不同表现型，然而这些表现型是由一组很大程度上共享的基因构建的。近年来，对许多动物的研究表明，基因表达的两性二态现象很常见，这提出了基因组中许多基因在两性中被选择为不同表达模式的可能性。然而，造成性别偏倚基因表达（SBGE）的选择机制却知之甚少。利用实验果蝇种群，我们将研究性别偏向基因表达（SBGE）在两种不同进化背景下的变化。首先，我们将研究SBGE是如何随着配偶竞争的变化而进化的，配偶竞争被认为是有利于二态性的主要力量。在第二部分中，我们研究了SBGE是如何在一种操纵下进化的，这种操纵使大部分基因组主要在一种性别中进化，从而大大减少了来自另一种性别的任何冲突选择。这项工作的一个主要目标是更好地了解已经二态表达的基因是否正在进行选择以获得更强的二态性，以及是否有许多基因目前不是二态的，但正在选择中变得如此。总的来说，这些项目将为SBGE的进化提供更清晰的画面，以及两种不同性别共享基因组进化的后果。

Sexual reproduction is widespread and, in most animals and some plants, involves two sexes. The long-term objective of the proposed research program is to understand the evolutionary causes and consequences of sexual reproduction, especially in systems with two sexes. One central aim is to quantify selection on sex and understand the various mechanisms by which this selection arises. The second aim is to understand the consequences of evolving with two separate sexes. One set of projects focuses on a plant that reproduces both sexually and asexually, the liverwort Marchantia polymorpha. We will study the population genomics of this species from different regions of North America to infer if populations vary in how frequently they reproduce sexually. If so, we will then infer whether higher rates of sex have positively influenced the efficacy of selection, as predicted. A second set of projects aims to understand selection on sex, one of the great unknowns of evolutionary biology. Well-established theory shows that selection on sex should work through how sex affects either the mean or the variance in fitness, yet there is almost no data evaluating these effects in nature. In a field study, we will measure the distribution of fitness of experimentally generated sexually- and asexually-derived offspring. Additional experiments will focus on testing key ecological sources of selection. A second set of projects focuses on differences between males and females. Selection often favours different phenotypes in the two sexes, yet these phenotypes are constructed from a largely shared set of genes. In recent years, studies in many animals have shown sexual dimorphism in gene expression is common, raising the possibility that many genes in the genome are selected for different expression patterns in the two sexes. However, the selection responsible for creating sex-biased gene expression (SBGE) is poorly understood. Using experimental fruit fly populations, we will examine changes in sex-biased gene expression (SBGE) in two different evolutionary contexts. In the first, we will examine how SBGE evolves in response to changes in mate competition, which is thought to be a major force favouring dimorphism. In the second, we examine how SBGE evolves in response to a manipulation that keeps a large portion of the genome evolving mostly in one sex, thereby greatly diminishing any conflicting selection from the other sex. One major goal of this work is to better understand whether genes that are already dimorphically expressed are under on-going selection for even stronger dimorphism and whether there are many genes that are not currently dimorphic but are under selection to become so. Collectively, the projects will provide a clearer picture of the evolution of SBGE and the consequences of evolving with a genome shared by two different sexes.