INFLUENCE OF MELATONIN ON GONAD MATURATION IN LINEUS-LACTEUS (HETERONEMERTINI, LINEIDAE)

The annual reproductive cycle of Lineus lacteus is regulated by photop eriod and thermoperiod. Gonad maturation depends on a gonad-inhibiting hormone (GIH) secreted by the cerebral ganglia, in which melatonin wa s also observed. Results in the worm showed that melatonin concentrati ons seemed to vary at the two most appropriate times of the year (spaw ning and sexual rest), in an inverse manner to the state of gonad matu ration. Exogenous melatonin did not significantly inhibit but delayed the advanced maturation of gonads triggered by decapitation of the wor m. We also showed that the GIH is not melatonin. We therefore assume t hat the gonad-inhibiting action of melatonin is indirect, and acts via the GIH. (C) 1996 Wiley-Liss, Inc.