Reproductive behavior of Aplysia californica Cooper: diel patterns, sexual roles and mating aggregations

Reproductive behavior of Aplysia californica Cooper was studied in the field and laboratory. Distinct diel patterns of behavior were found in the field. During the summer > 1/2 ofA. californica observed at 0300 and 0900 were engaged in reproductive behaviors (precopulatory behavior, copulations, egg-laying); feeding behavior predominated at 1500 and 2100. Relatively little time was spent crawling or being sedentary. This did behavior pattern was similar during two time periods spanning the summer peak in A. californica reproduction. A. californica mate in aggregations, which were larger at 0300 and 0900 than at 1500 and 2100. Larger aggregations and aggregations with eggs were more likely to persist to the following day than were small or egg-less aggregations. Despite the relatively high persistence ofmating aggregations, individual turnover within the aggregations was high only ~ 1/3 of the observed individuals were present in the same aggregation on the following day. Individuals usually joined mating chains as the terminal male, but left from either end or the middle. Mixed-species aggregations of A. californica and the sympatric A. vaccatia Winkler often formed, suggesting that the two species share a common sexual pheromone; however, the two species did not interbreed. A. californica are simultaneous hermaphrodites. The sexual role chosen by an individual was not a function of its mass, relative size compared to its partner, or immediate feeding history. Individuals of some Aplysia species have been reported to specialize in one or the other sexual role; A. californica did not. Egg-laying was associated with subsequent reproduction as a male; reproduction in either role was associated with subsequent egg-laying. The benefits of mating in aggregations probably drive A. californica diel behavior cycles and patterns of social interaction. Major differences in the behavior of different Aplysia species remain to be explained.