Chemical Studies of Natural Inducers of Larval Settlement and Metamorphosis for Two Species of Phestilla (Opisthobranchia)

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The objective of this research is to isolate and characterize the natural chemical inducers of larval settlement and metamorphosis for two related species of the nudibranch Phestilla. The two species consume scleractinian corals, but have different host preferences. The active molecules are potent morphogens, and profoundly influence the development of the nudibranchs. Natural inducers will be studied for Phestilla sibogae, which feeds on Porites corals, and P. melanobrachia, which feeds on dendrophyllid corals such as Tubastrea spp. Isolation of active compounds will be carried out by chromatographic separations of active extracts with subsequent bioassays of larval settlement to determine which fractions induce settlement and metamorphosis. Once purified, NMR and other spectroscopic methods will be used to elucidate the structures of active inducers. The chemical profiles of different species of corals can also be examined by analytical HPLC to determine whether the same active compounds are present in related corals. Comparison of the settlement cues for two related species of nudibranch will provide information on the ecology and evolution of host preference and the responses to soluble chemical cues for specialist marine invertebrates.