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.

lek悖论（lek paradox）是进化生物学中的一个理论问题：若由此产生的性选择（sexual selection）通过耗尽雄性间的遗传差异来限制雌性偏好，那么雌性对雄性质量的偏好如何得以维持？（Taylor & Williams 1982）该悖论不仅适用于求偶场物种（lekking species，即聚集在求偶场所的物种），还适用于任何受到强性选择的物种。针对这一悖论，已有若干解决方案被提出（例如Kirkpatrick & Ryan 1991；Dugand等2019），但令人惊讶的是，目前尚无实证证明lek悖论在自然界中真实存在（Ellegren & Galtier 2016）。换言之，受到更强性选择的物种其遗传多样性是否更低？为回答这一问题，我们比较了262种非飞行陆生哺乳动物的种群内遗传多样性（Miraldo等2016）——对于这些物种而言，雄性偏向的性二态性（male-biased sexual dimorphism）是衡量雄性所受性选择强度的良好指标（Soulsbury等2014）。在控制混杂效应后，我们发现雄性偏向性二态性更显著的物种其遗传多样性更低，这与性选择会削弱潜在配偶间遗传差异的预期一致。然而，这种关联并不强烈（β_st = -0.20），表明配偶遗传质量的差异并未被严重削弱。我们得出结论：至少部分针对lek悖论提出的解决方案在自然界中是有效的，且性选择可能仅在极少数情况下具有自限性。