The interplay of sexual selection and hybridization can drive sexual radiation

Many evolutionary radiations involve diversification of exaggerated sexual displays, but little is known about how they are formed. It has been theorized that there can be multiple stable equilibria in the evolution of sexually selected traits, by which multiple species having distinct sexual displays and mate preferences can stably persist. However, these theories alone do not fully explain the speciation process because the stability of each equilibrium will impede the formation of a new species from an existing species that is already occupying one of the stable equilibria. To explain the evolutionary process that forms species with diverse sexual displays, we here propose that hybridization between phenotypically similar but genetically divergent lineages can catalyse speciation by sexual selection, via the creation of genotypic and phenotypic variation. Using evolutionary simulations, we show that hybridization giving rise to variation in mate preference and sexual displays can alter the sexual selection regime, thereby creating opportunities for evolutionary shifts towards previously unoccupied stable equilibria. Thus, hybridization can facilitate evolutionary exploration of the stable evolutionary equilibria that sexual selection generates, leading to speciation accompanied by the diversification of exaggerated sexual displays.