A Metamorphic Inducer in the Opisthobranch Haminaea callidegenita: Partial Purification and Biological Activity

Larvae of Haminaea callidegenita (Mollusca: Cephalaspidea) were induced to metamorphose by a compound found in the gelatinous matrix composing most of the egg mass. A functionally similar compound isolated from adult tissue also induced metamorphosis in H. callidegenita larvae. Opisthobranchs are frequently induced to metamorphose by a specific prey item or a substrate characteristic of the adult habitat, but this is the first known instance of metamorphosis occurring in response to a compound produced by adult conspecifics. The inducer was purified from egg mass jelly (EMJ) by high pressure liquid chromatography (HPLC) and was found to be smaller than 1000 Da, polar, non-proteinaceous, and very stable. We isolated a compound of identical activity from egg masses produced by four other opisthobranch species, suggesting that the same or chemically similar compounds are intrinsic to opisthobranch egg masses. However, only H. callidegenita larvae metamorphosed in response to EMJ. Competent larvae of five other mollusc species did not respond to the partially purified EMJ inducer but did respond to a specific substrate associated with each species. The presence of the inducer within the egg mass causes an unusual developmental pattern in H. callidegenita, a poecilogonous species that produces both swimming veliger and crawling juvenile offspring.