MEPS 267:209-218 (2004)  -  doi:10.3354/meps267209

ABSTRACT: The inductive compounds that are cues for for the settlement and metamorphosis of polychaete Hydroides elegans larvae, isolated from adult homogenate of the same species and leachate of the bryozoan Bugula neritina, are known to be a mixture of amino acids. Here we investigated the toxicity of 20 amino acids on competent larvae. Nine amino acids were found to be toxic at certain concentrations. Subsequently, 12 out of 20 amino acids were assayed for their effect on larval metamorphosis of H. elegans. The effects of amino acids were decoupled from possible inductive effects of the bacteria in the bioassay system. The results showed that the amino acid isoleucine had no inductive effect on larval metamorphosis. Two acidic and 9 aliphatic amino acids directly induced larval metamorphosis. The effects of these amino acids were concentration-dependent. Among them, asparagine was the most active amino acid, and induced a high percentage of larval settlement at 1.0 × 10^-5 M, but became toxic at concentrations higher than 1.0 × 10^-4 M. The exact mechanisms by which amino acids directly induce larval metamorphosis are still unclear, although we assume that they act by binding to specific receptors and triggering the signal transduction pathway entirely or partially.

KEY WORDS: Hydroides elegans · Larval metamorphosis · Chemical cue · Amino acid · Bacteria