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, e.g., 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.