Catecholamines modulate metamorphosis in the opisthobranch gastropod Phestilla sibogae

Larvae of the nudibranch Phestilla sibogae are induced to metamorphose by a factor from their adult prey, the coral Porites compressa. Levels of endog enous catecholamines increase 6 to 9 days after fertilization, when larvae become competent for metamorphosis. Six- to nine-day larvae, treated with t he catecholamine precursor L-DOPA (0.01 mM for 0.5 h), were assayed for met amorphosis in response to coral inducer and for catecholamine content by hi gh-performance liquid chromatography. L-DOPA treatment caused 20- to 50-fol d increases in dopamine, with proportionally greater increases in younger l arvae, so that L-DOPA-treated larvae of all ages contained similar levels o f dopamine. A much smaller (about twofold) increase in norepinephrine occur red in all larvae. The treatment significantly potentiated the frequency of metamorphosis of 7- to 9-d larvae at low concentrations of inducer. In add ition, L-DOPA treatment at 9 d increased aldehyde-induced fluorescence in c ells that were also labeled in the controls, and revealed additional cells. However, all labeled cells were consistent with the locations of cells sho wing tyrosine-hydroxylase-like immunoreactivity. Catecholamines are likely to modulate metamorphosis in P. sibogae, but rising levels of catecholamine s around the time of competence are insufficient alone to account for sensi tivity to inducer in competent larvae.