The Role of Light and Endogenous Factors in the Timing of the Reproductive Cycle ofTyposyllis proliferaand some other Polychaetes

Abstract

SYNOPSIS. Reproductive processes in the syllid polychaete Typosyllis prolifera take an annual, a lunar-monthly and a daily pattern. Natural light changes (the seasonal change in relative daylength, the cycle of moonlight, the daily light-dark cycle) seem to provide the principal environmental information for the synchronization of reproduction with the external cycles. Both relative solar daylength and the daily light-dark cycle probably act exogenously. Moonlight, in contrast, acts as an entraining zeitgeber to a circalunar clock. Hormones (at least two distinct factors) mediate between the controlling centers and the peripheral tissues involved in sexual development. The effects of daylength and, indirectly, moonlight upon sexual development are brought about through the intermediation of the endocrine system. The exogenous and endogenous mechanisms of reproductive timing in T. prolifera are compared with those recently reported in some other polychaete species.