Male Mate Choice and Female Ornamentation; A Mathematical Model

Abstract.  Observations of male mate choice are increasingly common, even in polygynous species. In addition, female traits that bear the hallmarks of secondary sexual characters are increasingly reported. These concurrent empirical trends have lead to the repeated inference that, even under polygyny, male mate choice is a mechanism of sexual selection on female traits. We point out that this inference represents a testable hypothesis, for which the theoretical foundation remains largely uninvestigated. Females might experience sexual selection under polygyny if they compete for mates that provide either direct or indirect benefits. 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 co-exist in a population without any sexual selection 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 is quite weak. We discuss the implication of these findings for ongoing empirical and theoretical research on the evolution of sexual-signaling in females.