Spawning and gamete follicle rupture in the cnidarian Renilla koellikeri: effects of putative neurohormones.

The neuroendocrine control of spawning (release of intact gamete follicles) and of the ensuing exfoliation (freeing of gametes by follicle epithelium rupture) was investigated in colonies of the sea pansy Renilla koellikeri, an octocorallian of the sea pen family. Polyps of male colonies produce substantially more sperm follicles than female colonies do egg follicles, and significantly more sperm follicles are expelled than egg follicles during the summer spawning season. Spawning is accompanied by strong peristaltic contractions across the colony. Serotonin, a positive modulator of peristalsis in the sea pansy, induced spawning of either sperm or egg follicles, increasing both the proportion of spawning colonies and the number of expelled gamete follicles per colony in a dose-dependent manner. The serotonin antagonist 1-(1)naphthylpiperazine greatly reduced both spontaneous and serotonin-induced spawning. Antho-RFamide, a neuropeptide found in ciliated neurons within follicle epithelia, induced the exfoliation of the follicle epithelium from spawned follicles. Exposure of follicles to light enhanced the potency of Antho-RFamide. The actin-binding toxin phalloidin substantially reduced the incidence of Antho-RFamide-induced exfoliation and phalloidin-FITC staining was localized in the muscle feet of follicle epithelial cells. These results provide the first experimental evidence of neuroendocrine functions involved in cnidarian spawning.