Role of secondary metabolites in feeding associations between a predatory nudibranch, two grazing nudibranchs, and a bryozoan

Abstract

The carnivorous nudibranchRoboastra tigris preys preferentially upon two nudibranchs,Tambja abdere andT. eliora, that in turn feed upon the bryozoanSessibugula translucens. All four organisms contain tambjamines A–D (I–IV) that were shown to be fish feeding inhibitors. When attacked byRoboastra, T. abdere secretes a distasteful mucus containing a total of 3 mg of the tambjamines that sometimes causes theRoboastra to break off the attack. Under similar circumstancesT. eliora attempts to swim away; it presumably contains insufficient of the tambjamines to deterRoboastra. Roboastra follows the slime trail of nudibranchs using contact chemoreception and reverses direction when the trail is broken. The slime trail ofT. abdere contains low concentrations of the tambjamines. In Y-maze experiments,T. eliora was attracted towards seawater containingS. translucens and seawater containing 10⁻¹⁰ M tambjamines A and B (1∶1) but was repelled by seawater containing > 10⁻⁸ M tambjamines A and B. At higher concentrations the mixture of tambjamines may be recognized as an alarm pheromone.