Multiple mating, sperm storage, and mating preference in Aplysia californica.

Aplysia californica, a simultaneous hermaphrodite, has the ability to store and digest allosperm and frequently mates with multiple partners. Using controlled matings and behavioral observations, we characterized the mating behavior of multiply-mated A. californica. Regardless of their initial mating role, all animals mated a second time. Individuals acting as the initial sperm donor showed no preference for second mating role when paired with a "virgin" partner. However, individuals acting as the initial sperm recipient showed a highly significant preference for acting as the sperm donor in subsequent matings, when paired with a "virgin" partner. This preference disappeared when the initial sperm recipient spawned a fertilized egg mass prior to the second mating bout. On average, singly mated animals laid 2.85 +/- 0.39 (mean +/- SE, n = 13) egg masses before accepting sperm from a second donor. These results support the notion that depletion of stored allosperm plays a crucial role in the resolution of sexual conflict and the mating decisions of A. californica.