Data from: Male mate choice, male quality, and the potential for sexual selection on female traits under polygyny.

Observations of male mate choice are increasingly common, even in species with traditional sex roles. In addition, female traits that bear the hallmarks of secondary sexual characters are increasingly reported. These concurrent empirical trends have led to the repeated inference that, even under polygyny, male mate choice is a mechanism of sexual selection on female traits. It is often either assumed or argued that in these cases females are competing for males of superior “quality”; females might experience sexual selection under polygyny if they compete for mates that provide either direct or indirect benefits. However, the theoretical foundation of this testable hypothesis remains largely uninvestigated. We develop a population genetic model to probe the logic of this hypothesis and demonstrate that, contrary to common inferences, male mate choice, variation in male quality (in the form of a direct fecundity benefit to females), and female ornamentation can coexist in a population without any sexual selection on female ornamentation taking place at all. Furthermore, even in a “best case scenario” where high quality males with a preference for ornamented females are able to mate disproportionately more often with them, the evolution of female traits by sexual selection may be relatively weak. We discuss the implication of these findings for ongoing empirical and theoretical research on the evolution of sexual-signaling in females.

即便在具有传统性角色分工的物种中，关于雄性配偶选择（male mate choice）的观测记录也正变得愈发常见。此外，带有第二性征（secondary sexual characters）典型特征的雌性性状也日益被报道。这些并行出现的实证研究趋势，使得学界反复推导出如下结论：即便在一夫多妻制（polygyny）下，雄性配偶选择仍是作用于雌性性状的性选择机制。此类研究通常会假设或提出观点：在上述场景中，雌性会为争夺优质雄性展开竞争；若雌性为获取配偶所提供的直接或间接收益而竞争，则其可能在一夫多妻制下遭遇性选择。然而，这一可被验证的假说的理论基础，迄今仍未得到充分研究。本研究构建了种群遗传模型（population genetic model）以探究该假说的内在逻辑，结果表明：与普遍推论相悖的是，雄性配偶选择、雄性质量差异（以对雌性的直接繁殖力收益形式体现）以及雌性装饰性状，可在种群中共存，且完全无需对雌性装饰性状施加性选择。进一步而言，即便在“最优情境”下——即偏好雌性装饰性状的优质雄性，能以不成比例的更高频率与装饰性雌性交配——通过性选择驱动的雌性性状演化强度仍可能相对较弱。本研究还讨论了上述发现对当前开展的雌性性信号演化相关实证与理论研究的启示意义。