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.

有限种群中的无性生殖与高度自交物种，其选择作用的功效往往被削弱。这类种群被认为会随时间推移出现适合度下降，原因在于不断积累轻微有害突变，或是无法适应环境变化。这类种群内的过程会导致不重组物种走向灭绝，这一机制或可通过物种水平选择维持有性生殖与异交。尽管已有研究提出，低效选择会随时间推高灭绝速率，但此前针对有性生殖的物种选择模型均假设分化速率恒定。经典模型中，要使有性生殖得以存续，需满足无性类群的分化速率低于有性类群；这一前提无论在概念层面还是实证层面都存在争议。本研究对既往模型进行拓展，允许无性类群的分化速率随类群衰老而下降，即不重组类群的分化速率会出现“衰老”现象。在平衡状态下，即使年轻无性类群的分化速率快于其有性祖先类群，这种分化速率衰老的机制仍可维持有性生殖的存续。在此类场景中，无性类群的年龄分布会在中间龄期出现峰值，而非经典模型所预测的指数式下降。此时仅需满足无性类群的平均分化速率低于有性类群，二者即可实现共存。