INDUCTION OF LARVAL SETTLEMENT AND METAMORPHOSIS BY PHARMACOLOGICAL AND CONSPECIFIC ASSOCIATED COMPOUNDS IN THE SERPULID POLYCHAETE HYDROIDS ELEGANS

Field populations of the serpulid polychaete Hydroides elegans occur i n dense aggregations. Preliminary laboratory assays showed that plankt onic larvae H. elegans from Hong Kong waters did not settle and metamo rphose without proper chemical cues and could remain planktonic up to 14 d in laboratory culture. Adult H. elegans capture conspecific larva e with feeding tentacles but cannot readily consume older, competent l arvae. Contact between adult feeding tentacles and larvae may increase larval exposure to adult associated inductive compounds. In this stud y, we tested the effects of homogenates of adult worms and their tubes , as well as a variety of artificial inducers, on settlement and metam orphosis of H. elegans larvae. Conspecific adult homogenates induced 3 9 and 82% of larvae to settle and metamorphose within a period of 2 an d 4 d, respectively. Homogenates of the adult tube alone did not induc e settlement, indicating that the inducer originates from the worm, Ex traction and assays on crushed adult homogenates revealed that the ind uctive compounds from adults are smaller than 10 000 daltons and can b e bound to amberlite XAD-7. Further isolation and identification of th e conspecific associated inducer will enable studies of chemoreceptors and signaling pathways involved in metamorphosis. Additionally, among 5 artificial inducers tested, isobutyl methylxanthine (IBMX) induced a high percentage of normal metamorphosis while gamma-aminobutyric aci d (GABA), choline chloride, dihydroxyphenyl L-alanine (L-DOPA), and po tassium chloride evoked a low percentage of settlement, but abnormal m etamorphosis. Ammonia had no effect on the metamorphosis of H. elegans .