Linking Bioturbation and Sensory Biology: Chemoreception Mechanisms in Deposit-Feeding Polychaetes

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Soft-sediment benthic habitats are ubiquitous in the marine environment and typicallyfeature macrofaunal assemblages that include large numbers of deposit-feeding invertebratessuch as polychaetes, bivalves, gastropods, crustaceans, holothurians, and hemichordates. Viatheir feeding, modulated in part by chemoreception, these organisms have profound effects onthe ecology, biology, geology, and chemistry of their habitats. Very little is known, however,concerning the physiology and molecular biology of chemoreception in deposit feeders. This research is a comprehensive investigation of the sensory mechanisms coordinatingchemoreception in deposit feeding spionid polychaetes. It directly addresses this lack ofinformation and will therefore have a significant impact on the current understanding ofchemoreception in polychaetes and other marine invertebrates. In the first of three objectives, the ultrastructure and innervation of putative sensory structures on spionid polychaete palps will be described using electron and confocal microscopy. Second, the chemoreceptive capacity of palp sensory cells and nuchal organs will be tested withbehavioral assays and activity-dependent cell labeling studies. The behavioral assays will identify chemical cues that elicit significant feeding responses and establish their threshold sensitivities. Complementary immunocytochemistry experiments will determine (1) if the chemicals that elicit behavioral responses activate the sensory cells described in objective 1; (2) the sensitivity of the sensory cells (i.e., stimulation thresholds); and (3) the distribution of cells responding to a particular chemical cue. Third, a functional biochemical approach will be used to characterize and isolate candidate chemoreceptor proteins associated with the peripheral sensory cells and nuchal organs. Several outcomes of the research are of particular significance. First, the cell-labeling method will be further refined for use with small invertebrates, and will provide a powerful tool for future studies of the neural mechanisms coordinating habitat selection by many species of marine invertebrate larvae. Second, the sequence information and purified receptor will set the stage for development of mRNA and antibody probes that can be used to examine gene expression and detail the chemosensory transduction pathways in polychaetes and other marine invertebrates. Such information will be useful to researchers interested in the evolutionary relationships among invertebrate phyla and the in evolution of sensory structures. In addition to its scientific relevance, the project provides significant opportunities for graduate and undergraduate student training. Three K-12 educators or high school students will also participate through the Maine Research Internships for Teachers and Students program. Their participation not only increases the capacity of this over subscribed program, but also strengthens the links between the local K-12 community and the University of Maine. Internet activities and resources will be created that focus on sensory perception and ecology in the marine environment. These materials will extend the research to an even larger Internet audience and facilitate the incorporation of ocean science examples into topics typically approached only from a terrestrial and human perspective.