Possible roles of pheromones in inducing spawning of 2 brittle stars, Ophiocoma dentata and Ophiocoma scolopendrina, were tested with gonad homogenates. In both species, the ovary homogenate induced conspecific, competent males to spawn. The potential pheromone was speciesspecific and had no effect on conspecific females. The testis homogenate did not have any effect. Of the males 50% could be induced at an estimated concentration of 7.8 × 10 -7 g ml -1 (wet ovary weight/seawater) with a threshold concentration at 10 -8 g ml -1 . Some males could be induced to spawn at least 3 consecutive times at 1 d intervals. The unidirectional induction, i.e. males induced by female releasate, suggests high selective pressure of sperm limitation in these 2 species.

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