ABSTRACT: Diterpene metabolites produced by Dictyota species are known to inhibit feeding by several herbivorous species. We present the first evidence of feeding-deterrence of dictyotacean metabolites of an unusual compound belonging to a dichotomane diterpene skeleton type. Through experimental assay, we provide evidence of feeding-deterrent properties of lipid-soluble extracts of the Brazilian brown alga D. menstrualis (Hoyt) Schnetter, Hörnig & Weber-Peukert against the amphipod Parhyale hawaiensis Dana. Bioassay fractionation of this extract revealed the deterrent activity to be due to the diterpenoid (6R)-6-hydroxydichotoma-3,14-diene-1,17-dial, which was found to be the second most abundant metabolite (~0.2% dry mass) in D. menstrualis. In contrast to other studies, the major diterpenoid pachydictyol A, present as 0.4% (dry mass) in D. menstrualis, showed no anti-feeding properties. Our results suggest that chemical defense of Dictyota species may vary according to geographic region, thus explaining the presence of a metabolite other than pachydictyol A which functions as the anti-feedant metabolite in D. menstrualis from the Brazilian littoral zone.

KEY WORDS: Amphipod · Chemical defense · Dictyota menstrualis · Herbivory · Parhyale hawaiensis · Diterpenes

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Published in MEPS Vol. 205 (2000) on October 19
ISSN: 0171-8630. Copyright © Inter-Research, Oldendorf/Luhe, 2000