Evidence of a defensive role for limatulone, a novel triterpene from the intertidal limpet Collisella limatula

Collisella limatula, a limpet found abundantly in the rocky intertidal from Oregon to Baja California, has recently been found to contain a novel triterpene, llmatulone The present paper describes laboratory experiments and field observations that strongly suggest that limatulone acts as a potent chemical defense against some intertidal predators. Intertidal fish and crabs rejected pieces of the foot of C. limatula, but readily ate the foot tissue of CO-occurring gastropods. In contrast, individuals of C. limatula were eaten by seastars, an octopus and sea gulls. Fish antl-feedant activity was restricted to a slngle compound, limatulone, which was present In the foot of the limpet at a mean concentration of 3 5 ppt dry weight. Food pellets containing limatulone at concentrations of 2 0.5 ppt dry weight induced regurgitation in the intertidal fish Gibbonsia elegans, a known llmpet predator. Concentrations of limatulone in C. limatula varied from one geographic location to the next and from one mo to the next. Reasons for these variations are not understood Surveys of the 5 most common limpets in an undisturbed rocky intertidal site revealed that C, llmatula was the most abundant llmpet inside tidepools and on intertidal boulders. Limatulone may act to defend foraging limpets from predatory fishes In tidepools In the boulder field habitat, shell damage lncurred by limpets from wave-borne rocks and debris may expose foot tissue prior to shell regeneration, during which time the chemical defense may release C. limatula from predatory constraints imposed on other Intertidal limpets.