Lek Paradox

The lek paradox is a theoretical problem in evolutionary biology: how to sustain female preferences for male quality if the resulting sexual selection limits female preferences by depleting genetic differences among males (Taylor & Williams 1982)? The paradox applies not only to lekking species (i.e., those gathering in courtship arenas), but also to any species under strong sexual selection. Several solutions were proposed for this paradox (e.g., Kirkpatrick & Ryan 1991; Dugand et al. 2019) but, surprisingly, there is no empirical demonstration yet that the lek paradox exists in nature (Ellegren & Galtier 2016). In other words, is genetic diversity lower in species under stronger sexual selection? To answer this question, we compared within-population genetic diversity (Miraldo et al. 2016) across 262 spp. of non-flying terrestrial mammals, for which male-biased sexual dimorphism is a good indicator of sexual selection on males (Soulsbury et al. 2014). We found that more male-biased dimorphic species are less genetically diverse, controlling for confounding effects, in agreement with the expectation that sexual selection erodes genetic differences among potential mates. However, this association was not strong (β_st = -0.20), indicating that differences in mate genetic quality are not strongly eroded. We conclude that at least some of the proposed solutions for the lek paradox are efficient in nature, and that sexual selection may only rarely be self-limiting.