Data from: Aging asexual lineages and the evolutionary maintenance of sex

Finite populations of asexual and highly selfing species suffer from a reduced efficacy of selection. Such populations are thought to decline in fitness over time due to accumulating slightly deleterious mutations or failing to adapt to changing conditions. These within-population processes that lead non-recombining species to extinction may help maintain sex and outcrossing through species level selection. Although inefficient selection is proposed to elevate extinction rates over time, previous models of species selection for sex assumed constant diversification rates. For sex to persist, classic models require that asexual species diversify at rates lower than sexual species; the validity of this requirement is questionable, both conceptually and empirically. We extend past models by allowing asexual lineages to decline in diversification rates as they age, i.e., non-recombining lineages “senesce” in diversification rates. At equilibrium, senescing diversification rates maintain sex even when asexual lineages, at young ages, diversify faster than their sexual progenitors. In such cases, the age distribution of asexual lineages contains a peak at intermediate values rather than showing the exponential decline predicted by the classic model. Coexistence requires only that the average rate of diversification in asexuals be lower than that of sexuals.无性生殖与高度自交物种（asexual and highly selfing species）的有限种群，其选择效率会出现衰减。这类种群被认为会随时间推移出现适合度下降，原因在于轻微有害突变（slightly deleterious mutations）的累积，或是无法适应变化的环境条件。这类导致无重组物种（non-recombining species）灭绝的种群内过程，或可通过物种水平选择（species level selection）助力有性生殖与异交（outcrossing）的维持。尽管低效选择被认为会随时间推移提高灭绝速率，但过往针对有性生殖的物种选择模型，均假设分化速率（diversification rates）保持恒定。经典模型要求无性生殖物种的分化速率低于有性生殖物种，方能维持有性生殖的存续；但从理论概念与实证层面来看，这一要求的合理性均存疑。我们对过往模型进行拓展，允许无性生殖谱系（asexual lineages）随自身演化时长增加而出现分化速率下降，即无重组谱系的分化速率会发生“衰老”（senesce）。在平衡状态下，即便年轻的无性生殖谱系的分化速率快于其有性祖先，随衰老降低的分化速率仍可维持有性生殖的存续。在此类情境中，无性生殖谱系的年龄分布会在中间年龄段出现峰值，而非如经典模型所预测的那样呈现指数式衰减。两类生殖方式的共存仅需满足：无性生殖类群的平均分化速率低于有性生殖类群。