Sexual conflict coevolution - population size, divergence and the emergence of new variation

选择在生物多样性产生中的作用是一个令人兴奋和有争议的话题。人们早就认识到，对新环境的适应可以导致新形式的进化，但最近人们对性选择的潜力，特别是推动快速进化的性冲突产生了极大的兴趣。这一理论认为，男性不断面临压力，需要进化出新的方法来操纵他们的伴侣，以便他们更多地投资于特定男性的后代，而不是他们过去或未来的任何伴侣。反过来，雌性处于强势选择之下，以重新控制自己的繁殖，并优化自己的繁殖成功，而不是配偶的繁殖成功。有一些证据表明存在种内军备竞赛，但性别冲突在多大程度上能够推动快速进化和种群分化的关键问题仍然研究得很少，几个关键问题仍然几乎完全被忽视，特别是：1.种群规模对性别冲突驱动的进化有多重要？2.小种群之间的分化更快了，因为通过遗传漂移随机丢失等位基因很重要。或者在大种群中，因为有更多的突变输入和更多的常态遗传变异？3.突变输入是否会导致种群适应速度的变化，或者常态变异的水平总是更重要？这些问题对于试图理解变异的起源和维持的生物学家来说是非常有意义的。它们还对保护和圈养繁殖方案的设计产生了影响，在这些方案中，饲养更大的种群的成本更高，但可能保留更多的遗传变异，并经历更高的总体突变投入。研究对抗性共同进化的一个主要问题是，逆适应往往掩盖了推动它们进化的适应。例如，一种新的促进产卵的雄性精液化学物质可能只能通过观察雄性对其伴侣的影响来识别。然而，一旦雌性进化出对雄性化学物质缺乏敏感性，就不再可能检测到适应或反适应。在这项提案中，我们使用了一种新的方法来揭示这种变异：我们利用了一群自然具有大量性冲突驱动的适应和反适应的斑腿甲虫。我们的研究始于我们在强制一夫一妻制(雌性和雄性只允许一次配偶)条件下饲养了超过7年(90代以上)的种群。这些一夫一妻制的种群将失去许多冲突适应能力和大部分遗传多样性。我们将通过创造一系列允许自然交配制度的新种群，包括男性和女性之间的利益冲突，将性选择和性冲突重新引入这一系统。这些实验种群将包括总体种群大小和初始遗传变异水平不同的复制。我们将每隔一段时间检查新的冲突人口与基线一夫一妻制人口的交叉，以揭示新的冲突适应和冲突特征的重新建立，这些冲突特征由于消除了一夫一妻制的选择优势而减少到较低的频率。在30代之后，我们将在种群之间进行杂交，以获得在我们的研究期间进化的生殖隔离程度的直接测量，以及种群规模和遗传多样性对这一过程的影响。我们的研究将揭示性别冲突推动进化的速度有多快，这如何转化为种群之间的分歧(物种形成的燃料)，以及种群规模和遗传变异性对对抗性共同进化速度的影响。

The role of selection in the generation of biodiversity is an exciting and controversial topic. It has long been recognised that adaptation to new environments can lead to the evolution of new forms, but recently there has been great interest in the potential for sexual selection and in particular sexual conflict to drive rapid evolution. The theory is that males are under constant pressure to evolve new ways to manipulate their mates so that they invest more in the offspring of that particular male rather than any of their past or future mates. Females in turn are under strong selection to regain control over their reproduction and optimise their own reproductive success rather than that of their mate's. There is some evidence for intraspecific arms-races but the key question of the extent to which sexual conflict can drive rapid evolution and population divergence remains poorly studied and several key issues remain almost completely neglected, particularly: 1. How important is population size in promoting or retarding evolution driven by sexual conflict? 2. Is divergence faster between small populations because random loss of alleles through genetic drift is important, or in large populations because there is greater mutational input and more standing genetic variation? 3. Can mutational input cause populations to vary in the rate of adaptation or is the level of standing variation always more important? These questions are of great interest to biologists attempting to understand the genesis and maintenance of variation. They also have implications for the design of conservation and captive breeding programmes where larger populations are more expensive to rear, but may retain more genetic variation and experience higher overall mutational inputs. A major problem in studying antagonistic coevolution, is that counter-adaptations often mask the adaptations which have driven their evolution. For instance a new male seminal chemical that accelerates egg laying might only be identified by observing the effects of males on their partners. However, once females evolve lack of sensitivity to the male chemical, it no longer becomes possible to detect either the adaptation or the counter-adaptation. In this proposal we use a novel approach to reveal such variation: we utilise a population of beetles Callosobruchus maculatus that naturally have substantial sexual conflict driven adaptations and counter-adaptations. Our study begins with populations that we have been keeping for over 7 years (90+ generations) under conditions of enforced monogamy (females and males only allowed a single mate). These monogamy populations will have lost many of their conflict adaptations and much of their genetic diversity. We will re-introduce sexual selection and sexual conflict to this system by creating a range of new populations where the natural mating regime is allowed, including conflicts of interest between males and females. These experimental populations will include replicates that differ in overall population size, and initial levels of standing genetic variation. We will examine populations at intervals crossing the new conflict populations with the baseline monogamy population to reveal new adaptations to conflict and the re-establishment of conflict traits that have been reduced to low frequencies by the removal of their selective advantages in the monogamy lines. After 30 generations we will conduct crosses between populations to gain direct measures of the degree of reproductive isolation that has evolved during our study and the influence that population size and genetic diversity has had on this process. Our study will reveal how rapidly sexual conflict can drive evolution, how this can translate into divergence between populations (the fuel for speciation) and the influences of population size and genetic variability on the rate of antagonistic coevolution.