The effect of size,age, and recent egg laying on copulatory choice of the hermaphroditic mollusc Aplysia juliana

Summary

Aplysia juliana is a cross-fertilizing, simultaneous hermaphrodite. During copulation, an individual may act as either a sperm donor or a sperm recipient, or both, when a pair copulates reciprocally. Experiments were conducted with A. juliana to determine if an animal's size, age, or recent egg-laying activity influenced its choice of copulatory role. Animals were isolated except when paired during daily, half-hour trials. In the first experiment, mature animals of different size (weight) but similar age were randomly paired. Animal size had no effect on the initial copulatory role chosen. In the second experiment, young, maturing A. juliana were paired with older animals. Young animals showed no preference in initial copulatory role either as a group or individually. Older A. juliana showed no copulatory preference as a group, but over half of the individuals demonstrated a consistent choice of one role. Some individuals acted almost exclusively as sperm donors, others as sperm recipients, suggesting that as an A. juliana ages, it is likely to develop a preference for a single copulatory role. A record of daily egg mass production was kept for all animals in the second experiment. Production of an egg mass since the last copulation did not affect the copulatory role chosen in the subsequent copulation.