Data from: Evolutionarily stable sex ratios and mutation load

Frequency-dependent selection should drive dioecious populations toward a 1:1 sex ratio, but biased sex ratios are widespread, especially among plants with sex chromosomes. Here, we develop population genetic models to investigate the relationships between evolutionarily stable sex ratios, haploid selection, and deleterious mutation load. We confirm that when haploid selection acts only on the relative fitness of X and Y-bearing pollen and the sex ratio is controlled by the maternal genotype, seed sex ratios evolve toward 1:1. When we also consider haploid selection acting on deleterious mutations, however, we find that biased sex ratios can be stably maintained, reflecting a balance between the advantages of purging deleterious mutations via haploid selection, and the disadvantages of haploid selection on the sex ratio. Our results provide a plausible evolutionary explanation for biased sex ratios in dioecious plants, given the extensive gene expression that occurs across plant genomes at the haploid stage.

频率依赖选择（frequency-dependent selection）本应推动雌雄异株（dioecious）种群的性比趋近于1:1，但偏性比却广泛存在，尤其在具有性染色体的植物类群中更为常见。为此，我们构建种群遗传模型，以探究进化稳定的性比、单倍体选择（haploid selection）与有害突变负荷（deleterious mutation load）之间的关联关系。我们证实，若单倍体选择仅作用于携带X、Y染色体的花粉相对适合度，且性比由母本基因型调控，则种子性比将进化至1:1。然而，当我们同时纳入作用于有害突变的单倍体选择因素后，发现偏性比可被稳定维持——这反映了通过单倍体选择清除有害突变的益处，与单倍体选择对性比造成的不利影响之间的动态平衡。鉴于单倍体阶段在植物基因组中存在广泛的基因表达现象，我们的研究结果为雌雄异株植物的偏性比现象提供了合理的进化解释。