Chemical ecology of some opisthobranch mollusks

Typescript.Thesis (Ph. D.)--University of Hawaii at Manoa, 1983.Bibliography: leaves 119-125.Microfiche.xvii, 125 leaves, bound ill. 29 cmMany opisthobranch mollusks (Class Gastropoda, Subclass Opisthobranchia) are shell-less, slow moving invertebrates, and are ostensibly unprotected and vulnerable to predation. Observations have shown, however, that these shell-less mollusks are rarely, if ever, eaten. The phenomenon is at least in some cases a result of defense secretions by opisthobranchs. Five nudibranch species were investigated chemically. Additionally, three of the principal food sources for three of the nudibranch species were subjected to parallel investigations. Different degrees of correlation were found between the metabolites of the predator-prey pairs, and all nudibranchs were found to contain high concentrations of specific metabolites. Structure elucidation was performed by spectral analysis and chemical transformation. Indoles 1 to 7 and hōkupurine (8) were isolated from extracts of the dendrophyllid coral Tubastrea coccinea. Indoles 3 to 7 and hōkupurine (8) were identified from the aeolid nudibranch Phestilla melanobrachia, which lives and feeds exclusively on T. coccinea. P. melanobrachia also contained large amounts of an unstable heteroaromatic base (9), which was not found in the coral, and may be a defensive secretion. Specimens of the dorid nudibranch Dendrodoris nigra and Dendrodoris tuberculosa contained a mixture of polygodial (10) and olepupuane (11) in their skin extracts. The dorid nudibranch Chromodoris elisabethina contains the potent fish toxin latrunculin-A (12) in its skin extracts. Latrunculin-A is a sponge metabolite, but was not isolated from the chief food source of this dorid, the sponge Heteronema sp. Puupehenone (13) was isolated as the major constituent of Heteronema sp. Hypselodoris infucata is known to feed on the sponge Dysidea fragilis. Surface extracts of H. infucata yielded a mixture of nakafuran-8 (14) and -9 (15), previously isolated from Dysidea and other dorid nudibranchs