Measuring how sexual selection history impacts on population viability under genetic stress

当一种性别的个体（通常是男性）为繁殖成功而竞争时，就会发生性选择。达尔文首先认识到性选择是一种力量，它可以通过雄性与雄性之间的竞争、雌性的选择或两者兼而有之，导致复杂性状的进化，帮助它们的携带者获得个体生殖成功。自从这些早期的启示，我们已经意识到，性选择可能会对个体的大多数特征和基因起作用，因为在面对环境压力时实现生殖成功需要一系列功能特征尽可能适应。正因为如此，性选择可能相对有效地从种群中筛选出携带不完美基因或有害突变的个体，我们现在对性状如何通过性选择进化，以及哪些因素解释了个体繁殖成功的动力学有了很多了解，但我们在了解性选择对种群的影响方面投入的精力要少得多。这种缺乏关注的情况需要改变，因为正是人口的生存能力支撑着生物多样性和生态系统的稳定，而这两个方面现在都因人类活动而遭受前所未有的、不断加剧的环境压力。因此，该项目将衡量性选择对于创造在压力面前具有上级生存能力的种群的重要性。我们的一般方法将是使用一些独特的拟谷盗粉甲虫，我们已经仔细保持在控制条件下5年在UEA，其中唯一的因素，我们已经通过实验改变的强度和形式的性选择。因此，这些品系将经历65代的实验进化，它们已经揭示了个体雄性和雌性如何适应不同水平的性选择的一些重要见解。我们现在建议使用这些线来衡量历史的高，中，低和没有性选择，使人口抵抗灭绝时，他们被放置在近亲繁殖的遗传压力。在近亲繁殖的情况下，当基因相关的个体被迫繁殖时，有害的突变更有可能暴露在后代中。因此，这种情况提供了一个揭示性的措施，潜在的突变负荷，人口携带。近亲繁殖现在被认为是自然环境中的一种相关力量，因为种群变得紧张和枯竭，导致种群完全消失的“灭绝漩涡”。我们的假设是，在更高水平的性选择下维持的实验种群，在那里雄性有更大的机会：男性竞争和女性选择，应该更有效地清除有害的基因突变，因此，在近亲繁殖的压力下，将保持较高的生产力和对灭绝的更大抵抗力。我们的生产力测试将测量在标准和恶劣环境中每对雄性雌性产生的后代数量，我们的生存能力测试将测量灭绝率。当我们通过兄妹配对来提高近亲繁殖水平时，我们将看到我们的实验种群随着生产力的降低而变得越来越不可行，最终走向灭绝。我们预测，过去有过性选择历史的种群，应该比没有或很少有性选择历史的种群，在更长的时间内保持生产力和抵抗灭绝。我们的发现不仅将为性选择如何从基因组中过滤有害突变提供有价值的实验见解，而且还将告知性选择的重要性，性选择是自然环境中维持承受日益增加的压力的小种群的遗传健康的宝贵力量。

Sexual selection occurs when individuals of one sex (usually males) compete for reproductive success. Darwin first recognised sexual selection as an force which could cause the evolution of elaborate traits that helped their bearers to gain individual reproductive success, either through male:male competition, female choice, or both. Since these early revelations, we have come to realise that sexual selection probably acts on most of an individual's traits and genes, because achieving reproductive success in the face of environmental stress requires a whole range of functional traits to be as adaptive as possible. Because of this, sexual selection might be relatively effective at filtering out individuals from a population who carry imperfect forms of genes or deleterious mutations.We now know a great deal about how traits evolve through sexual selection, and what factors explain the dynamics of individual reproductive success, but we have placed far less effort into understanding the population consequences of sexual selection. This lack of attention needs to be changed, because it is population viability which underpins biodiversity and ecosystem stability, both of which are now suffering unprecedented and accelerating environmental stress as a result of human activities. This project will therefore measure the importance of sexual selection for creating populations that have superior viability in the face of stress. Our general approach will be to use some unique lines of Tribolium flour beetles which we have carefully maintained under controlled conditions for 5 years at UEA, and where the only factor we have experimentally varied is the intensity and form of sexual selection. These lines will have therefore been subjected to experimental evolution across 65 generations, and they have already revealed some important insights into how individual males and females become adapted to different levels of sexual selection. We now propose to use these lines to measure how histories of high, medium, low and no sexual selection render populations resistant to extinction when they are placed under the genetic stress of inbreeding. Under inbreeding, when genetically related individuals are forced to reproduce, deleterious mutations are more likely to be exposed in offspring. This situation therefore provides a revealing measure of the underlying mutational load that a population is carrying. Inbreeding is now recognised to be a relevant force in the natural environment as populations become stressed and depleted, contributing to an 'extinction vortex' where populations can completely disappear.Our hypothesis is that experimental populations which have been maintained under higher levels of sexual selection, where there are greater opportunities for male:male competition and female choice, should have been more effectively purged of deleterious genetic mutations, and so will maintain higher productivity and greater resistance to extinction under the stress of inbreeding. Our tests of productivity will be to measure the number of offspring generated per male-female pair in standard and poor environments, and our test of viability will be to measure extinction rates. As we increase the inbreeding level through sib-sib pairings down advancing generations, we will see our experimental populations becoming less viable as they reduce their productivity, and eventually go extinct. We predict that populations with a past history of heightened sexual selection should maintain productivity and resist extinction for longer than populations with no or low histories of sexual selection.Our findings will not only provide valuable experimental insight into how sexual selection can filter deleterious mutations from the genome, but will also inform on the importance of sexual selection as a valuable force in the natural environment for maintaining the genetic health of small populations that are subjected to increasing stress.