ASYMMETRY OF MALE AND FEMALE MATING IN MIXED-SPECIES GROUPS OF APLYSIA FASCIATA POIRET AND APLYSIA BRASILIANA RANG (MOLLUSCA: GASTROPODA)

ABSTRACT

Aplysia fasciata and A. brasiliana are found on opposite sides of the Atlantic Ocean, but are morphologically and behaviorally very similar. To determine the relationship between these two species, mating patterns were examined in single-species and mixed-species groups of 2 and 4 individuals. In single—species groups, A. brasiliana spent less time mating than did A. fasciata. However, the relative distribution of time spent mating as a male, as a female, or in both sexual roles simultaneously was virtually identical in both species. The overall time spent mating in mixed-species groups was similar to that seen in single-species groups of A. brasiliana, and was significantly less than in single-species groups of A. fasciata. In mixed-species groups there were relative increases in the likelihood for A. fasciata to mate as males, and for A. brasiliana to mate as females. Our data indicate that when animals with differing sexual drives are in contact, the animal with the stronger sexual drive generally mates as a male. This suggests that the level of mating is set by a drive to mate as a male, while female mating is largely nonselective and passive. The data also indicate that A. fasciata and A. brasiliana are either somewhat different populations of the same species, or are very closely related species.