Data from: Loss of sexual recombination and segregation is associated with increased diversification in evening primroses

The loss of sexual recombination and segregation in asexual organisms has been portrayed as an irreversible process that commits asexually-reproducing lineages to reduced diversification. We test this hypothesis by estimating rates of speciation, extinction, and transition between sexuality and functional asexuality in the evening primroses. Specifically, we estimate these rates using the recently developed BiSSE (Binary State Speciation and Extinction) phylogenetic comparative method, which employs maximum likelihood and Bayesian techniques. We infer that net diversification rates (speciation minus extinction) in functionally asexual evening primrose lineages are roughly eight times faster than diversification rates in sexual lineages, largely due to higher speciation rates in asexual lineages. We further reject the hypothesis that a loss of recombination and segregation is irreversible because the transition rate from functional asexuality to sexuality is significantly greater than zero.and in fact exceeded the reverse rate. These results provide the first empirical evidence in support of the alternative theoretical prediction that asexual populations should instead diversify more rapidly than sexual populations because they are free from the homogenizing effects of sexual recombination and segregation. Although asexual reproduction may often constrain adaptive evolution, our results show that the loss of recombination and segregation need not be an evolutionary dead-end in terms of diversification of lineages.

无性生殖生物丧失有性重组与染色体分离的过程，一贯被视作不可逆进程，认为无性繁殖谱系的多样化水平会因此下降。我们以月见草属植物为研究对象，通过估算物种形成、灭绝以及有性生殖与功能性无性生殖之间的转换速率，对该假说开展实证检验。具体而言，我们采用新近开发的二元状态物种形成与灭绝（BiSSE, Binary State Speciation and Extinction）系统发育比较方法开展速率估算，该方法结合了最大似然法与贝叶斯推断技术。我们推断，功能性无性生殖月见草谱系的净分化速率（物种形成速率减去灭绝速率）约为有性生殖谱系的8倍，这一差异主要源于无性谱系更高的物种形成速率。我们进一步推翻了‘重组与分离丧失不可逆’的假说：功能性无性生殖向有性生殖的转换速率显著大于0，且实际高于反向转换速率。本研究首次提供实证证据，支持另一项理论预测：由于无需承受有性重组与染色体分离带来的同质化效应，无性种群的多样化速率应高于有性种群。尽管无性生殖往往会限制适应性演化，但本研究结果表明，就谱系多样化而言，重组与分离的丧失未必是演化死胡同。