The Eco-Evolutionary Dynamics of Sexual Traits That Increase Mate Encounter Rates

AbstractSexual selection theory focuses on variation in mating success caused by a shortage of mates relative to same-sex competitors, but variation in mating success can also arise if mates are limited in an absolute sense (e.g., due to low encounter rates). To assess the potential for absolute mate limitation to contribute to sexual trait evolution, we develop a quantitative genetic model of a costly trait that increases mate encounter rates but is expressed solely in the operationally limiting sex. We show that sexual selection favors the elaboration of such a trait provided the marginal increase in offspring production exceeds the marginal increase in mortality. The conditions in which this occurs depends on population dynamic variables that change as the trait evolves. The resulting eco-evolutionary dynamics generally cause the sexual trait to converge on a single eco-evolutionary equilibrium value that, once established, cannot be replaced. These findings suggest a broader set of ecological contexts in which sexual selection can in principle occur and highlight promising directions for future research on the eco-evolutionary dynamics of sexual selection, sexual coevolution, and causes of variation in mating success in the limiting sex.