Sexual selection on males predicts reduced mitochondrial genetic diversity across mammals

Sexual selection on males is expected to reduce genetic diversity via paternal inheritance because increased variance in male reproductive success lowers the male effective population size. It is plausible that sexual selection on males also affects genetic diversity via maternal inheritance, for example due to demographic processes. However, associations between sexual selection and maternally-inherited genetic diversity were never tested for. Here, taking advantage of the fact that mitochondria are maternally-inherited, we compare the diversity of two widely studied mitochondrial genes across 262 species of non-flying terrestrial mammals, for which male-biased sexual dimorphism is a good indicator of the intensity of sexual selection on males. We found that species with stronger male-biased dimorphism have lower mitochondrial diversity, after controlling for confounding effects. A plausible explanation for this result is that sexual selection on males can reduce female effective population size, giving rise to the change of allelic diversity in these mitochondrial genes. Our result thus suggests broader associations of sexual selection with demography and population genetic structure than previously recognized.

雄性所经历的性选择（sexual selection），理论上会通过父系遗传途径降低遗传多样性：雄性繁殖成功率的方差升高，会缩小雄性有效种群规模（male effective population size）。不过，雄性性选择也可能通过母系遗传途径影响遗传多样性——例如经由种群动态过程实现，这一推论具备合理性。但此前从未有研究检验过性选择与母系遗传的遗传多样性之间的关联。本研究借助线粒体（mitochondria）母系遗传的特性，以262种非飞行陆生哺乳动物为研究对象，以雄性偏倚的性二态性作为衡量雄性性选择强度的可靠指标，比较了两类被广泛研究的线粒体基因的多样性水平。在控制了混杂效应的影响后，我们发现雄性偏倚的性二态性越强的物种，其线粒体多样性越低。对于这一结果，一个合理的解释是：雄性所受的性选择会缩小雌性有效种群规模（female effective population size），进而导致这些线粒体基因的等位基因多样性发生改变。因此，本研究结果表明，性选择与种群动态及种群遗传结构之间的关联，比此前学界所认知的更为广泛。