INTERSPECIFIC VARIATION IN CHEMICAL DEFENSES IN THE SEA HARES (OPISTHOBRANCHIA, ANASPIDEA)

Most species of sea hares (Opisthobranchia: Anaspidea) sequester secon dary metabolites from their algal diets in their digestive glands. Apl ysia juliana Quoy and Gaimard, 1832, a sea hare that feeds on Ulva spp . and Enteromorpha spp., algae with few or no secondary metabolites, w ere compared with the sympatric sea hares A. oculifera Adams and Reeve , 1850, A. kurodai (Baba, 1937), and Dolabella auricularia (Solander, 1786), all of which eat chemically rich algae, to see if sequestered s econdary metabolites afford protection to sea hares from potential pre dators. Organic extracts of whole A. juliana stimulated, and organic e xtracts of whole D. auricularia deterred feeding by crabs. However, te sts with organic extracts of individual body parts indicated that this pattern was due almost exclusively to unpalatability of extracts of D . auricularia digestive glands. Tests with pieces of tissue from the e xterior of the animals, or with extracts of such tissues, showed no co nsistent patterns indicating that A. juliana were more palatable than other sea hares. Sea hare egg masses do not appear to contain diet-der ived secondary metabolites. However, pieces of egg masses of A. julian a and D. auricularia were universally rejected by crabs and reef fish, and extracts of A. juliana egg masses deterred feeding by some reef f ish. Finally, both opaline secretion of A. juliana and ink of A. kurod ai, but not ink of D. auricularia, none of which appear to contain die t-derived secondary metabolites, deterred feeding by crabs. Opaline se cretion from A. juliana, but not ink from A. kurodai, induced avoidanc e behavior in crabs. Although sequestered secondary metabolites clearl y can affect the palatability of the digestive gland, there is little evidence that they affect the palatibility of the ink, opaline secreti on, eggs, or skin, suggesting that sequestered secondary metabolites m ay not play a key role in anti-predator defense of sea hares.