AJP - Regulatory, Integrative and Comparative Physiology, Vol 260, Issue 5 839-R843, Copyright © 1991 by American Physiological Society
Emesis, learned aversion, and chemical defense in octocorals: a central role for prostaglandins?
D. J. Gerhart
Duke University Marine Laboratory, Beaufort, North Carolina 28516.
Prostaglandin A2 and its ester derivatives comprise as much as 8% of the
wet tissue weight of some octocoral species such as Plexaura homomalla
(phylum Cnidaria, class Anthozoa, subclass Octocorallia). These high levels
of prostaglandins, although initially palatable to fish, may function as
defensive toxins by inducing emesis and learned aversions in potential
predators. As the fish Fundulus heteroclitus and Halichoeres garnoti gain
experience through the course of experiments, they increasingly reject
foods containing emetic prostaglandins, but do not alter their acceptance
of untreated control foods. Emesis is also induced in fish by consumption
of tissue or lipid extracts from the subtropical whip coral Leptogorgia
virgulata (subclass Octocorallia, order Gorgonacea). The emetic properties
of L. virgulata induce learned aversions in the fish Micropterus salmoides
and Morone saxatilis. Extracts of L. virgulata do not contain high levels
of prostaglandins but do, however, contain other metabolites that appear to
mimic the effects of eicosanoids. Some nonprostanoid secondary metabolites
may induce emesis by stimulating prostaglandin biosynthesis in the gastric
mucosa of predators.
