Copulatory and post-copulatory mating behaviours depend on the mating status of both partners in a simultaneous hermaphrodite

Mating status is one of the most important predictors of the mating propensity of an individual. This is because mating lowers the amount of sperm cells and seminal fluids available to donate for males and increases the amount of ejaculate received by females, which may both have an effect on the mating propensity. In simultaneous hermaphrodites with reciprocal copulation, the mating status is expected to affect the mating propensity in both the male and the female sex function within a single individual, but empirical evidence is scarce. We experimentally tested the effect of the mating status of an individual and its partner on copulatory and postcopulatory behaviour in the free-living flatworm Macrostomum lignano, an outcrossing simultaneous hermaphrodite. These worms have frequent reciprocal copulations and often display a postcopulatory suck behaviour, potentially involved in removing ejaculate components from their own sperm-receiving organ. Virgin pairs copulated more, earlier and for longer than sexually experienced pairs. Moreover, we observed fewer sucks in virgin than sexually experienced pairs, all consistent with a higher willingness both to donate and to receive sperm in virgins. We investigated whether the lower suck frequency in virgin pairs depends on the mating status of the focal individual or on that of its partner. Surprisingly, the results suggested that the suck frequency depends on the mating status of the partner. We discuss these results in the context of potential sexual conflicts over the performance of the suck behaviour.