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，性选择就发生了。达尔文首先认识到，性选择是一种力量，可以导致精细特征的进化，帮助携带者获得个体生殖成功，无论是通过雄性竞争，还是雌性选择，或者两者兼而有之。自从这些早期的发现以来，我们开始意识到，性选择可能会影响一个人的大多数特征和基因，因为在面对环境压力时获得生殖成功需要一系列的功能特征尽可能地适应。正因为如此，性选择可能会相对有效地将携带不完美基因形式或有害突变的个体从种群中剔除。我们现在知道很多关于特征是如何通过性别选择进化的，以及什么因素可以解释个体生殖成功的动态，但我们在理解性别选择对种群的影响方面投入的努力要少得多。这种缺乏关注的情况需要改变，因为正是种群的生存能力支撑着生物多样性和生态系统的稳定，由于人类活动，这两者现在都遭受着前所未有的、正在加速的环境压力。因此，该项目将衡量性选择对于创造在压力下具有优越生存能力的种群的重要性。我们的总体方法将是使用一些独特的Tribolium面粉甲虫品系，这些品系是我们在UEA在受控条件下谨慎保持了5年的，我们在实验中改变的唯一因素是性选择的强度和形式。因此，这些品系将经历65代人的实验性进化，它们已经揭示了关于个体男性和女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系来衡量当种群处于近亲交配的遗传压力下时，高、中、低和无性选择的历史如何使种群抵抗灭绝。在近亲繁殖中，当基因相关的个体被迫繁殖时，有害突变更有可能在后代中暴露出来。因此，这种情况揭示了一个群体所携带的潜在突变负荷。近亲交配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，导致了种群可能完全消失的“灭绝漩涡”。我们的假设是，实验种群保持在更高水平的性别选择下，那里有更多的雄性竞争和雌性选择机会，应该更有效地清除有害的基因突变，从而在近亲交配的压力下保持更高的生产力和对灭绝的更大抵抗。我们对生产力的测试将是测量在标准和恶劣环境中每对雄性和雌性所产生的后代的数量，我们对生存能力的测试将是测量灭绝速度。随着我们通过兄弟姐妹配对来提高近亲繁殖水平，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，与没有或较少性选择历史的群体相比，过去有高度性选择历史的群体应该更长时间地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，而且还将告知在自然环境中，性选择作为维持承受越来越大压力的小群体遗传健康的一种宝贵力量的重要性。

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.