Cryptic female choice can maintain reproductive isolation

Sexual selection has long been considered an important mechanism of speciation. Despite growing empirical evidence that postmating sexual selection—selection on traits that affect fertilization—is common, most speciation theory has focused on premating sexual selection. Cryptic female choice can result in assortative fertilization, e.g., conspecific sperm precedence—a process where females bias fertilization towards conspecific males during sperm competition. Although there is empirical evidence of conspecific sperm precedence in a wide range of taxa, there is little theory on conspecific sperm precedence via cryptic female choice, limiting our understanding of how it contributes to speciation.  We use simulation models of secondary contact to ask under what circumstances conspecific sperm precedence can evolve and maintain reproductive isolation. We found that cryptic female choice alone can maintain reproductive isolation under limited but realistic conditions, specifically when the migration rate is low, cryptic preferences are strong, and multiple mating is intermediate. In combination with ecological divergence, cryptic female choice was able to maintain reproductive isolation even at high rates of migration. We also found that conspecific sperm precedence could evolve through reinforcement. Our results demonstrate that cryptic female choice could maintain reproductive isolation and, therefore, can contribute to species divergence and maintenance.