Meeting Abstract

93.6  Thursday, Jan. 7  How to Produce a Chemical Defense: Sea Hares Manufacture Antipredatory Chemicals from Diet-Derived Red Algal Photosynthetic Pigments KAMIO, Michiya; NUSNBAUM, Matthew; AGGIO, Juan; GRIMES, Tiphani; DERBY, Charles*; Georgia State University cderby@gsu.edu

In defense against predators, sea hares use an ink secretion composed of purple ink and white opaline. This colored secretion might protect sea hares through visual or chemical modalities. We used bioassay-guided fractionation to identify components in ink of Aplysia californica responsible for its defensive effect against blue crabs Callinectes sapidus, bluehead wrasses Thalassoma bifasciatum, and the spiny lobsters Panulirus argus and Panulirus interruptus. We used two behavioral assays: a feeding assay in which secretions were added to food, and a squirting assay in which secretions were released as clouds. For crabs and wrasses, ink was more effective than opaline, and two pigmented molecules in ink – aplysioviolin (APV) and phycoerythrobilin (PEB) – accounted for much of ink’s activity. APV and PEB were equally effective at equal doses, but APV is the major deterrent because of its much higher concentration. In contrast, for spiny lobsters, opaline is more effective than ink, and APV and PEB have little effect. Sensory ablations showed that ink secretion’s effects were mediated through chemical senses. Sea hares acquire the light-harvesting protein phycoerythrin from red algae, cleave the chromophore PEB from the protein, convert PEB to APV by methylation, and preferentially store APV in ink. Sequestering chemical defenses from food is a strategy of many animals, but converting a food-derived photosynthetic pigment into a chemical defense is novel. Why sea hares convert PEB to APV is currently unknown, since they are equally effective in defense against the predators that we have examined. The results of our and other studies show that sea hares use a diversity of molecules and mechanisms, some but not all diet-dependent, in chemically defending themselves against their many potential predators. Supported by NSF and Naval Surface Warfare Center – Panama City.