Sexual selection and mate limitation shape evolution of species' range limits.

Understanding what processes shape the formation of species' geographic range limits is one central objective linking ecology and evolutionary biology. One potentially key process is sexual selection; yet, theory examining how sexual selection could shape eco-evolutionary dynamics in marginal populations is still lacking. In species with separate sexes, range limits could be shaped by limitations in encountering mates at low densities. Sexual selection could therefore modulate mate limitation and resulting extinction-colonization dynamics at range margins, through evolution of mate encounter ability and/or mate competition traits, and their demographic consequences. We use a spatially explicit eco-genetic model to reveal how different forms of sexual selection can variably affect emerging range limits. Larger ranges emerged when sexual selection acted exclusively on traits increasing mate encounter probability, thus reducing female's mate limitation toward the range margins. In contrast, sexual selection via mate competition narrowed range limits due to increased trait-dependent mortality in males and elevated mate limitation for females. When mate encounter coevolved with mate competition, their combined effects on range limits depended on the mating system (polygyny vs. monogamy). Our results demonstrate that evolution of species' ranges may be importantly shaped by feedbacks between sexual selection and spatial population demography and dynamics.