Asymmetric barriers to gene flow can maintain sex role differentiation upon secondary contact

Acquiring a mate and providing parental care require substantial time and energy. Evolution typically favours allocating more effort to one of these actions at the expense of the other. Differences between the sexes in such allocation are common, with males investing more heavily in mate acquisition and females investing more heavily in parental care in systems with conventional sex roles and the converse pattern in sex-role-reversed systems. If populations diverge in sex roles, pre- or postmating incompatibilities may arise. For example, if different sexes provide parental care in different populations, interpopulation mating combinations may produce broods that receive little to no care, which could lead to low offspring survival. Here, we consider a two-patch model to ask whether variation in sex roles can persist upon secondary contact in populations that have diverged. We find that populations with sexes that are differently specialized in parental care versus sexual selection can, indeed, remain differentiated after secondary contact and, further, that the mechanism maintaining differentiation depends on the direction of dispersal. Importantly, however, whether populations remain diverged depends on both the model of mate acquisition and the resultant population dynamics (density dependence, mating rate, population size). These findings have potential implications for incipient speciation and the evolution of reproductive barriers.