Detection of juvenile hormone-active compounds by larvae of the marine annelidCapitella sp. I

Several bioassay systems have been previously developed to detect the presence of juvenile hormones or compounds with juvenile hormone-activity (JH activity). While investigating the effects of juvenile hormones on polychaete annelid development, we have previously found that metatrochophore larvae of the polychaete Capitella sp. I are induced to settle and metamorphose in response to compounds with JH-activity in less than 1 h. Investigating further the settlement-inducing effects of chemicals with varying degrees of JH-activity, we have found that there is a positive relationship between the JH-activity of chemicals in the Galleria insect cuticle bioassay and their ability to induce settlement and metamorphosis of the Capitella larvae. The juvenoids JH I, JH III, and methyl farnesoate induced 50% of the larvae to settle and metamorphose in 1 h at concentrations of 25, 12, and 1 μM dissolved in the seawater (EC50s). The JH-active fatty acid eicosatrienoic acid also was very active having an EC50 of 10 μM, whereas non-JH-active chemicals such as cholesterol and alkane hydrocarbons were not effective in inducing settlement and metamorphosis. These results therefore suggest that the Capitella settlement and metamorphosis assay may aid in the detection and purification of chemicals with JH-activity.