PIRES, A.*; GILBORN, A.C.: Catecholamines in metamorphosis of primitive gastropods.

Metamorphosis of molluscan veligers is usually induced by a chemosensory stimulus and includes stereotyped behaviors. Recently it has been shown that the induction of metamorphosis is modulated by catecholamine neurotransmitters, in the opisthobranch gastropod Phestilla sibogae. In an effort to determine if such modulation is likely to be an ancestral feature of gastropod metamorphosis, we have investigated this phenomenon in the primitive gastropods, Calliostoma ligatum (Trochidae) and Tectura scutum (Lottidae). Antibodies directed against the catecholamine-synthetic enzyme, tyrosine hydroxylase, labeled similar cells in cephalic tentacles and propodia of larvae of both species. Treatment of larvae with the catecholamine precursor L-DOPA (10-5 M for 0.5 h, followed by 3 h incubation in seawater) enhanced endogenous dopamine 14-fold in T. scutum and 9-fold in C. ligatum (n=4 and 6 batches of larvae, respectively, measured by HPLC with electrochemical detection). Endogenous norepinephrine doubled in T. scutum , and increased by 58% in C. ligatum . Surprisingly, norepinephrine was 4 times more abundant than dopamine in control larvae of C. ligatum , although it is much less abundant than dopamine in all other molluscs that have been examined. Competent control larvae of both species metamorphosed on biofilmed intertidal stones. In both species L-DOPA treatment failed to potentiate metamorphosis in response to this cue. However, L-DOPA-treated larvae of C. ligatum ,unlike seawater controls, metamorphosed at high frequencies on clean unfilmed polystyrene substrates. These results, taken together with earlier work on P. sibogae , point to substantial diversity in the deployment and function of catecholamines in the regulation of gastropod metamorphosis.