Larvae of a Nudibranch Mollusc (Phestilla sibogae) Metamorphose when Exposed to Common Organic Solvents

Abstract

Larvae of the nudibranch mollusc Phestilla sibogae metamorphosed when exposed to 10 of 14 organic solvents. The active solvents included five alcohols and ethanolamine, acetonitrile, acetone, dichloromethane, and toluene. Inactive solvents were ethylene glycol, DMSO, benzene, and hexane. These compounds span a wide range of polarities and contain a number of functional groups. Ethanol induced metamorphosis after 1-5 days of exposure at 0.5-0.001 M, and maximally induced about 65% of larvae to metamorphose in 3-5 days at 0.1 M. Ethanol was lethal to larvae above 0.75 M (ca. 4%). Methanol was lethal only above 1.75 M (ca. 7%), but produced less metamorphosis than ethanol at most concentrations. The natural inducer of metamorphosis in P. sibogae produced higher percentages of metamorphosis more rapidly than did any of the solvents. The mechanism of metamorphic induction by the solvents is not known, but they probably interfere with a wide range of neuronal activities and trigger an existing metamorphic pathway. Precompetent (young) larvae did not metamorphose in response to ethanol or methanol, but juveniles produced by exposure of competent (mature) larvae to ethanol or methanol survived to reproduce. Larvae of one other mollusc species also metamorphosed in response to ethanol, suggesting that larvae of other invertebrates may also be induced to metamorphose by organic solvents. Larval biologists should be aware of this possibility.