Endocrine mechanisms mediating light-temperature effects on male reproductive activity inTyposyllis prolifera (polychaeta, syllidae).

When exposed to a "winter" light-temperature cycle, reproduction in the polychaeteTyposyllis prolifera is inhibited by a hormone from the proventriculus. When exposed to a "summer" cycle, worms show periodic reproduction following an endogenous lunar rhythmictiy. The endocrine system mediating the stimulation of reproduction by summer conditions, was studied by extirpation and transplantation of prostomium and/or proventriculus. A previously unknown prostomial hormone was found to play a major role in this process. Summer conditions induce a temporary endocrine activity in the prostomium. This homone probably does not act directly on peripheral targets, but stimulates reproduction by inactivating the proventricular endocrine system. The experimental evidence of a hierarchic neuroendocrine system governing reproductive activity in syllid polychaetes is discussed.