Sexual selection and the origin of species: experimental insight into adaptation, the purging of deleterious mutations, and the evolution of sexual isolation

达尔文有着广为人知的广泛的研究兴趣，但其中最突出的是我的研究项目的两个分支：与性别和物种起源有关的选择。就前者而言，性选择发生在个体生殖成功不同的时候，它可以导致雄性和雌性在体型、外表和行为上的显著差异的进化。事实上，达尔文最初提出的性选择理论是为了解释这种差异的进化，最明显的特征是孔雀尾巴等在生存方面不适应的特征。在这中间的几年里，我们已经很好地理解了性选择在代价高昂的性特征进化中的作用。然而，关于性选择的其他基本方面的问题仍然没有得到回答，我的研究计划的第一个分支解决了其中的两个问题。首先，性选择是促进还是阻碍适应，其次，它是否有助于消除每一代人都会出现的有害突变？人们对性选择对非性健康的这些后果的关注有限，所做的工作往往涉及高度简化的实验室环境，这可能会提供有偏见的见解。我的提案描述了一系列实验，以测试性选择的各种群体遗传后果，以及这些结果是否以及如何依赖于环境的复杂性。 我的研究的第二个分支涉及新物种是如何出现的，从而说明了世界生物多样性的一个主要组成部分的起源。物种是由生殖障碍的存在来定义的，这些障碍限制了它们之间的遗传交流。性隔离的进化，即来自不同种群的个体作为潜在配偶彼此吸引较少，长期以来一直被认为是一个关键的生殖障碍，对启动和完成物种形成过程都很重要。尽管性隔离的存在是直截了当的，但要理解它的演变，就需要确定相关的潜在特征，以便我们能够确定它们是如何分化的。令人惊讶的是，即使在研究得最好的有机体群体中，导致性别隔离的特征也鲜为人知。我的提案概述了另外一系列实验，这些实验旨在全面了解一对北美食用菌苍蝇的性隔离原因，并在这样做的过程中解决物种形成研究中几个研究不足的问题。我的研究计划中的这两个分支都严重依赖于一种名为实验进化的强大技术，在这种技术中，我们比较不同条件下种群的进化过程是如何展开的。这项工作的结果将对我们对进化的基本理解产生广泛的影响，包括适应如何发生和生命多样性的产生。

Darwin had famously wide ranging research interests but preeminent among these were the two branches of my research program: selection in relation to sex and the origin of species. With respect to the former, sexual selection occurs when individuals differ in reproductive success and it can result in the evolution of striking differences between males and females in size, appearance, and behaviour. Indeed, Darwin originally proposed his theory of sexual selection to account for the evolution of such differences, most notably traits like the peacock’s tail that are maladaptive in terms of survival. In the intervening years, we have come to understand well sexual selection’s role in the evolution of costly sexual traits. However, questions concerning other fundamental aspects of sexual selection remain unanswered and the first branch of my research program addresses two of these. First, does sexual selection promote or hinder adaptation, and second, does it help in removing the harmful mutations that arise every generation in populations? Limited attention has been given to these consequences of sexual selection for nonsexual fitness and the work that has been done tends to involve highly simplified lab environments that may be providing biased insight. My proposal describes a series of experiments that test the various population genetic consequences of sexual selection and whether and how these depend on environmental complexity. The second branch of my research concerns how new species arise and thus speaks to the origins of a major component of the world’s biological diversity. Species are defined by the presence of reproductive barriers that restrict genetic exchange between them. The evolution of sexual isolation, whereby individuals from different populations are less attracted to one another as potential mates, has long been suggested to be a key reproductive barrier that is important in both initiating and completing the speciation process. Although the existence of sexual isolation is straightforward to demonstrate, understanding its evolution requires identifying the underlying traits responsible so that we can determine how they have diverged. Surprisingly, even in the best studied groups of organisms the traits causing sexual isolation are seldom known. My proposal outlines an additional series of experiments that build a comprehensive understanding of the causes of sexual isolation in a pair of N. America mushroom-feeding flies, and in doing so addresses several understudied topics in speciation research. Both branches on my research program rely heavily on a powerful technique called experimental evolution in which we compare how the evolutionary process unfolds in populations under different conditions. The results of this work will have broad implications for our basic understanding of evolution including how adaptation occurs and the diversity of life arises.