Factors influencing spawning and pairing in the scale worm Harmothoe imbricata (Annelida : Polychaeta)

Endocrine and environmental factors control reproduction of the polynoid sc ale worm Harmothoe imbricata. We confirmed that the rate of vitellogenesis was greater in winter specimens transferred from ambient regimes of photope riod and temperature to a light:dark (LD) photoperiod of 16:8 at 10 degrees C and showed that the number of females spawning was significantly greater than for those transferred to LD8:16 at 10 degrees C. The endocrine mediat ion of this response was investigated using prostomium implantations. Signi ficantly more LD8:16 females implanted with prostomia from LD16:8 condition ed females spawned than LDS:16 females implanted with LDX:16 prostomia. Fem ales without prostomia failed to spawn. LD16:8 exposure may increase levels of a possible "spawning hormone" in the prostomium. Spawning proceeded in these LD16:8 females and allowed spawning to occur in LD8:16 females implan ted with LD16:8 prostomia. In LDS:16 prostomia, titers of the spawning horm one reached the threshold in significantly fewer individuals, so that signi ficantly fewer females implanted with LD8:16 prostomia spawned. Using Y-maze choice chambers, pair formation was shown to be under pheromon al control, with males being attracted to mature females but not to females carrying fertilized oocytes or to LD8:16 conditioned females. Production o f this attraction pheromone can, therefore, be manipulated through photoper iodic control, suggesting a link between oogenesis, spawning, and pheromone production.