10 サンゴ幼生に作用する無節サンゴモの他感作用物質(口頭発表の部)

抄録

Most benthic marine invertebrates have a planktonic larval stage in their life cycle, and then larvae settle and metamorphosis into adult form. In Cnidarians, metamorphosis is naturally triggered by external cues and not by the elevation of an internal hormone level as in amphibians or insects. Various species of crustose coralline red algae (CCA) and bacterial biofilms have been shown to be the primary sources of external inducers of metamorphosis for coral larvae. We have focused on the relationship between CCA and coral larvae mediated by their metabolites. In our observational study, a fragment of coral rubble with CCA induced larval metamorphosis of the scleractinian coral Pseudosiderastrea tayamai, however coral larvae didn't settle on directly surface of the CCA. These results suggested that coral rubble with CCA have two types of chemical signals i.e., defense chemical and natural inducer. We have established a simple bioassay using P. tayamai larvae for such biological phenomena. The methanol extract of coral rubble with CCA showed toxic activity against the coral larvae. Bioassay-guided isolation of methanol extract afforded two new brominated toxic compounds, corallinafuran (1, 10^<-6>M) and corallinaether (2, 10^<-7>M). In contrast, the natural inducer and compounds that enhanced its effect in larval metamorphosis were isolated from methanol extracts of same coral rubble with CCA. A bromotyrosine derivative, 11-deoxyfistularin-3 (3, 10^<-7>M) isolated from the CCA, induced the metamorphosis of P. tayamai larvae (22.2±22.2%). In the presence of fucoxanthinol (4, 10^<-9>M) and fucoxanthin (5, 10^<-9>M), the percentage of metamorphosis induced by 3 was further enhanced to 88.9±13.6 and 94.4±13.6%, respectively. Both carotenoids are also found in the coral rubble with CCA. These results suggest that bromotyrosine derivative and carotenoids have a synergistic effect in the metamorphosis of P. tayamai larvae. This effect may provide a higher selectivity for recruitment than a single-component natural inducer for recognizing suitable substrata for larval metamorphosis. Thus, the effect might offer a survival advantage for benthic marine invertebrates.