LARVAL SETTLEMENT AND METAMORPHOSIS OF HYDROIDES ELEGANS IN RESPONSE TO CHEMICAL CUES
Qian, P.-Y.
Hong Kong University of Science & Technology, Clear Water Bay, Hong Kong
The tube building polychaete Hydroides elegans occurs in dense aggregations and often attaches to colonies of the arborescent bryozoan Bugula neritina in Hong Kong waters. Laboratory assays showed that H. elegans larvae require proper chemical cues to settle and metamorphose; the larvae either settled and metamorphosed in response to conspecific cues or extracts/leachate of B. neritina or biofilm. With aid of rigorous bioassay-guided isolation and purification procedures, conspecific cues have been identified to be a group of amino acids. Compounds extracted from the leachate of B. neritina induced very high percentage of H. elegans larvae to settle and appears to be different compounds in nature from conspecific cues. Larval settlement in response to 12 isolated bacterial strains was species-specific. Bacterial films combined with different bacterial strains at different proportions also affected larval settlement. Bioassays with supernatant of the bacterial broth culture revealed that inductive cues were not released into the medium but, presumably, bound to the bacterial cell surfaces. Addition of D-glucose solution into bacterial treatment almost entirely blocked the larval settlement. This confirmed the previous finding that recognition of bacterial cells by H. elegans larvae might involve lectin-like receptors that could be blocked by glucose on the larval surface. Our results suggest that larvae of H. elegans may settle in response to a broad range of chemical cues. Current studies in my laboratory are to identify these chemical cues and to study chemoreceptors and signaling pathways involved in metamorphosis.