Chemical ecology of the Antarctic nudibranch Bathydoris hodgsoni Eliot, 1907: defensive role and origin of its natural products.

Abstract A variety of Antarctic marine invertebrates contains secondary metabolites that may provide defense against potential predators. However, only in a few cases have tissues, extracts or isolated compounds of these invertebrates been tested against sympatric predators. The Antarctic nudibranch Bathydoris hodgsoni Eliot, 1907 contains hodgsonal, a compound only present in the external body (mantle tissues), which may protect the slugs from predators. To test this defensive hypothesis for hodgsonal, we carried out a series of experiments using the sympatric omnivorous seastar Odontaster validus Koehler, 1906 as a potential predator. Our experiments revealed that natural concentrations of hodgsonal elicit significant feeding deterrent responses in O. validus . Furthermore, hodgsonal is probably biosynthesized de novo by the nudibranch, since it was not detected in the viscera (as it should be in the case of a dietary compound), its concentration in the mantle (0.05–0.15% dry mass) is quite constant in individuals from different localities and depths, and its sequestration from a particular dietary source is unlikely because B. hodgsoni is an omnivorous feeder.