Artificial induction of larval metamorphosis by free fatty acids

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Abstract
Larvae of the marine polychaete Phragmatopoma californica attach and metamorphose upon contact with conspecific tubes. By providing adults with clean silanized glass beads with which they built tubes, uncontaminated tube-material which induced metamorphosis was obtained. This allowed partial purification of the natural inducer of metamorphosis without maceration or extraction of biologically contaminated tubes collected from the field. Evidence is presented that free fatty acids are not responsible for the natural gregarious attachment and metamorphosis of larvae in P. californica, as had been suggested by other work. (1) Clean prepartions of the natural inducer contain no free fatty acids. Yields of free faty acids in extracts from field-collected tubes are dependent on the extent of biological contamination of the sample. (2) All of the carbon present in the natural inducer is accounted for (within experimental error) as protein. (3) Upon organic solvent extraction, activity is decreased for both the natural inducer and palmitoleic acid coated glass beads. However, unlike palmitoleic acid coated glass beads, extraction of natural inducer with organic solvents yields no free fatty acids, indicating inactivation of a labile inducer by this process, rather than extraction of a fatty acid. (4) In confirmation of the last point, lyophilization and stirring decrease activity of the labile natural inducer; both have no effect on the activity of palmitoleic acid coated glass beads. (5) Induction of metamorphosis by palmitoleic acid is temperture-dependent; induction by conspecific tubes is not. (6) Induction by the natural inducer is taxon-specific, but induction by fatty acids is not. The behavior of Haliotis rufescens (red abalone) larvae, which attach and metamorphose upon contact with crustose coralline algae, is not affected by exposure to tubes of P. californica. However, exposure of abalone larvae to certain free fatty acids results in dose-dependent behavioral and physiological responses, including a low level of attachment and metamorphosis. Based on evidence presented here and the known biological activity of free fatty acids in signal transduction and membrane perturbation in other systems, it is suggested that free fatty acids induce metamorphosis by operating physiolgoically downstream or parallel to the natural inducer. It is probable that free faty acids in extracts of material containing macerated worms and other biological material are artifacts, liberated by lipolytic enzymes from these tissues, and not part of any natural system that induces settlement, attachment, or metamorphosis.

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