Data from: Stabilizing selection, mutational bias and the evolution of sex

Stabilizing selection around a fixed phenotypic optimum is expected to disfavor sexual reproduction, since asexually reproducing organisms can maintain a higher fitness at equilibrium, while sex disrupts combinations of compensatory mutations. This conclusion rests on the assumption that mutational effects on phenotypic traits are unbiased, that is, mutation does not tend to push phenotypes in any particular direction. In this paper, we consider a model of stabilizing selection acting on an arbitrary number of polygenic traits coded by bialellic loci, and show that mutational bias may greatly reduce the mean fitness of asexual populations compared with sexual ones in regimes where mutations have weak to moderate fitness effects. Indeed, mutation and drift tend to push the population mean phenotype away from the optimum, this effect being enhanced by the low effective population size of asexual populations. In a second part, we present results from individual-based simulations showing that positive rates of sex are favored when mutational bias is present, while the population evolves towards complete asexuality in the absence of bias. We also present analytical (QLE) approximations for the selective forces acting on sex in terms of the effect of sex on the mean and variance in fitness among offspring.围绕固定表型最优值的稳定化选择通常被认为不利于有性生殖，因为无性生殖生物在平衡状态下可维持更高的适合度，而有性生殖会破坏补偿突变的组合。该结论基于一项核心假设：突变对表型性状的效应无偏，即突变不会倾向于将表型推向任意特定方向。本文针对由双等位基因座编码的任意数量多基因性状构建稳定化选择模型，结果显示，在突变具有弱至中等适合度效应的情形下，突变偏倚可能大幅降低无性生殖种群的平均适合度，使其低于有性生殖种群。事实上，突变与遗传漂变往往会推动种群平均表型偏离最优值，而无性生殖种群较低的有效种群大小会加剧这一效应。在第二部分中，我们展示了基于个体的模拟结果：当存在突变偏倚时，有性生殖的正频率会受到选择青睐；而在无偏突变的条件下，种群会演化至完全无性生殖状态。我们还基于有性生殖对后代适合度均值与方差的影响，推导了作用于有性生殖的选择压力的解析（准连锁平衡，Quasi-Linkage Equilibrium，缩写QLE）近似解。