Sperm storage and use in laboratory-reared Aplysia californica , a simultaneous hermaphrodite

Abstract

Aplysia californica, an opisthobranch mollusc, possesses a complex reproductive system that includes a seminal receptacle for the storage of exogenous sperm received from mating. Based on this reproductive anatomy, A. californica should have the ability to maintain and use viable exogenous sperm stores to fertilize multiple eggmasses for extended periods of time. Using controlled matings and careful observation of the development of eggmasses over time, we attempted to quantify A. californica’s ability to store and use exogenous sperm following a single mating. On average, A. californica (240.6±31.7 g; mean±SE, n=9) produced 8.8±0.6 eggmasses containing 16.9±2.2×106 fertilized eggs over a period of 22.3±3.6 days following a single mating encounter. The maximum duration an individual A. californica produced fertilized eggs, following a single copulation, was 41 days. The primary factor determining the cumulative number of fertilized eggs produced from a single mating in A. californica was the mass of the sperm recipient (r=0.773, P<0.05, n=9). Our results demonstrated that A. californica are not sperm limited following a single mating as has been suggested for other opisthobranch molluscs by Leonard and Lukowiak’s (1991) gamete-trading hypothesis.