The Biological Bulletin, Vol 181, Issue 1 81-94, Copyright © 1991 by Marine Biological Laboratory

BEHAVIOR

Relative Contributions of the Egg Layer and Egg Cordon to Pheromonal Attraction and the Induction of Mating and Egg-laying Behavior in Aplysia

S. D. Painter, M. G. Chong, M. A. Wong, A. Gray, J. G. Cormier and G. T. Nagle
The Marine Biomedical Institute and the Department of Anatomy and Neurosciences, University of Texas Medical Branch, Galveston, Texas 77550-2781

Many species of the opisthobranch mollusk Aplysia form breeding aggregations during the reproductive season. The aggregations contain both mating and egg-laying animals, and are associated with egg cordons. Although pheromones play a significant role in developing and maintaining the aggregations, little is known about the active factors. Behavioral studies have shown that egg-laying animals are more attractive than nonlaying animals, have shorter latencies to mating, and induce conspecifics to lay eggs. As a first step toward isolating and chemically characterizing the active factors, we examined the relative importance of the egg layer and egg cordon as sources of pheromonal activity in Aplysia brasiliana. T-maze experiments showed that both animal-derived and cordon-derived factors are attractive, and that the animal-derived factors are specifically associated with egg layers. Extracts of the atrial gland--an exocrine organ secreting into the oviduct--increased the attractiveness of nonlaying animals when placed in the surrounding seawater, suggesting that the "cordon-derived" aggregation pheromones may be products of the atrial gland. Mating studies showed that both animal-derived and cordon-derived factors induce mating, and that the animal-derived factors are associated with both egg layers and nonlayers. In contrast, neither animal-derived nor cordon-derived factors induced egg laying. Comparable results were obtained with either one or two animals in the chamber, suggesting that the accessibility of a potential mate did not influence the results. The lack of effect may result from the low-probability nature of egg-laying activity.

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