A Two Phase Photoperiodic Response Controlling the Annual Gametogenic Cycle in Harmothoe imbricata (L.) (Polychaeta: Polynoidae)

Summary

In the polychaete Harmothoe imbricata, a photoperiodic mechanism stabilises oogenesis during its early stages and prevents oocyte breakdown. During the autumn, photoperiods of 14 hr light per day or more cause the animals to abort gametogenesis and resorb their oocytes. Conversely, photoperiods of 13 hr or less stabilise gametogenesis and allow normal oocyte growth. The length of the exposure required to stabilise gametogenesis and prevent abortion lies between 42 and 55 days. This effect is in addition to a previously described phenomenon causing accelerated oocyte growth in the spring in response to moderately long photoperiods. The interaction between these two different photoperiodic responses is discussed.