Divergent mating system adaptations in microallopatric populations of Acanthodiaptomus denticornis (Copepoda, Calanoida)

Abstract

Ecological differentiation, sexual selection and sexual conflict have been proposed as speciation drivers in copepods, but empirical support is scarce. Because sexual conflict is common in the suborder Calanoida, we tested whether sexual selection drives differentiation between populations. We conducted mating experiments between two geographically adjacent but morphologically different populations of the calanoid copepod Acanthodiaptomus denticornis from the French lakes Lac Pavin and Lac de Montcineyre. We detected sex-specific inter-population differences in mating success. In particular, Lac de Montcineyre males (M males) exhibited a higher mating success in short matings than Lac Pavin males (P males). In contrast to M females, P females showed population-density-dependent fecundity. Furthermore, survival of P females decreased in inter-population groups. We suggest that planktivorous glassworm larvae, which inhabit only Lac de Montcineyre, impose selection on copulating pairs of copepods. This may adaptively increase the ability of M males to fertilize eggs during short matings and indirectly decrease sensitivity of M females to male coercion. The former adaptation might result in a fitness disadvantage of P male immigrants in Lac de Montcineyre, whereas the latter redefines a "battleground" for population-specific sexual conflict. Both ecological adaptation and sexual conflict may contribute to divergence in our study system.