| Recent S-022 Research at McMurdo Station | |
1. To study the chemical defenses in eggs, embryos and larvae of antarctic marine invertebrates.
We have found that the ovaries, eggs, embryos or larvae of five species of benthic marine invertebrates with lecithotrophic modes of reproduction are unpalatable or chemically defended from ecologically relevant sympatric sea star, sea anemone and amphipod predators (McClintock and Baker, 1997b). The planktotrophic eggs or larvae of two additional species were not chemically defended.
2. To investigate the role of pigments in antarctic invertebrate chemical defenses.
Pigments from Latrunculia apicalis (discorhabdins; Yang et al., 1995), Kirkpatrickia variolosa (variolins; McClintock and Baker, 1997a) and Dendrilla membranosa (quinolone; Baker et al., 1995), displayed ecologically relevant bioactivity (see McClintock and Baker, 1997a), including tube-foot retraction (indicative of feeding deterrence (McClintock et al., 1994a) and antimicrobial activity using sympatric microorganisms. Eribusinone, from Isodictya erinacea (Moon et al., 1998) was studied as a molt inhibitor due to its structural similarity to the crustacean molt inhibitor 3-hydroxykynurenine. The voracious amphipod predator Orchomene plebs consumed more artificial food impregnated with a sponge extract enriched in eribusinone (to an ecologically relevant concentration) than controls; in addition, O. plebs molt incidence was reduced with a concomitant increase in mortality (Baker and McClintock, unpublished work in progress). This is the first demonstration of molt inhibition as a mechanism of chemical defense in the marine realm.
3. To examine the tissue-specific sequestering or concentration variations among tissues of bioactive compounds in sessile and sluggish antarctic marine invertebrates.
We investigated Marseniopsis mollis, and Parborlasia corrugatus for tissue specific sequestration of bioactive compounds. M. mollis contains homarine throughout its tissues (mantle, foot, viscera), while P. corrugatus sequesters a protein toxin in mucous secretions. The sponge Suberites sp. has been found to concentrate the tube-foot deterrent suberitenone A and B (Baker et al., in press) in its outer-most tissues, which is the first demonstration of sponge cell differentiation with regard to secondary metabolism (Baker, Barlow and McClintock, unpublished work in progress).
4. To isolate and identify bioactive compounds from antarctic marine invertebrates, to examine their role as feeding deterrents, and to evaluate their dietary or other origin.
To date we have isolated and identified more than three dozen secondary metabolites from bioactive extracts of antarctic organisms. Antarctic sponges have been the most productive, being the source of 25 of these metabolites. Some we have shown to cause feeding deterrence in ecologically relevant predators, some are potent antimicrobial agents, one is known as a plant growth regulator, and several of the metabolites are cytotoxic.
We have investigated invertebrate extracts and secondary metabolites in ecologically relevant feeding deterrent and antimicrobial assays. Pure compounds from six sponge species were evaluated in a behavioral tube-foot retraction (TFR) assay designed to identify the presence in sponge extracts of chemistry deterrent toward the major sponge predator, Perknaster fuscus (McClintock et al., 1994a; submitted). Neither the nor-diterpenes nor the pigment isolated from Dendrilla membranosa showed deterrent activity in the TFR assay; picolinic acid is likely the active component of this sponge (Baker et al., 1995). Discorhabdin C, from Latrunculia apicalis, was significantly active in this assay (Yang et al., 1995) as was an as yet unidentified dark purple pigment from Kirkpatrickia variolosa; variolin A was not deterrent toward P. fuscus. Sea star deterrent activity was observed in the polar extract of Isodictya erinacea; one isolate, p-hydroxybenzaldehyde, was active at ecological concentrations. The cytotoxin rhapsamine Leucetta leptorhapsis (Baker et al., 1993; Jayatilake et al., 1997) demonstrated TFR activity, as did suberitenones A and B from Suberites sp. (Baker et al., in press). The omnivorous sea star Odontaster validus is a potential predator of a number of antarctic benthic invertebrates. We used this animal as the basis of a feeding deterrent assay for metabolites from the gastropods Tritoniella belli (McClintock et al., 1994b) and Marseniopsis mollis (McClintock et al., 1994c). Homarine, from M. mollis, and chimyl alcohol, from T. belli, both caused rejection of shrimp-treated disks at natural tissue-level concentrations.
We examined crude extracts and several pure compounds in antimicrobial screens (Baker et al., 1993) utilizing standard laboratory microorganisms as well as sympatric marine microorganisms. Discorhabdin C, from the sponge Latrunculia apicalis, and the pigment from the sponge Dendrilla membranosa, proved to be the most active antimicrobial compounds. We have shown that select sponge metabolites (Yang et al., 1995) and associated bacteria can inhibit water-column and sponge-derived microorganisms (Thornton, 1995). Steroidal glycosides from the sea star Acodontaster conspicuus were effective antibiotic agents toward sympatric marine microorganisms (De Marino et al., 1997) as is a polar metabolite recently isolated from the sponge Guitarra sigmatifera (Baker, Furrow and McClintock, unpublished).
The antarctic mollusc Clione antarctica, which is the unwitting guest of the hyperiid amphipod Hyperiella dilatata (McClintock and Janssen, 1990), produces the novel ichthyodeterrent (Bryan et al., 1995) pteroenone (Yoshida et al., 1995).
Contribution to the Development of Human Resources: During the granting periods one high school student, eleven undergraduates, ten graduate students, and two postdoctoral associates participated. To date, seven of the eight graduate students have co-authored papers, as did postdoctoral associates, and a total of three MS theses and three doctoral dissertations resulted from the funded programs. In 1996, a High School Physics Teacher was selected by NSF to work with our group in Antarctica. This teacher developed a world wide web page that provided daily information to teachers and students on aspects of our research program and published a CD-ROM describing the experience. To date aspects of our NSF-funded research have appeared in a number of media outlets including National Geographic, Discover Magazine, International Wildlife, Science News, NPR Radio, scientific sections of the Los Angeles Times, Chicago Tribune, Birmingham Post-Herald, Florida Today and Washington Post, and a children's science book ("Science on the Ice: An Antarctic Journal" by Rebecca Johnson, Lerner Publ. Co. 1996).
Go to summary of current work at Palmer Station
Go to peer-reviewed references
Go to non-peer-reviewed references