Date of Award

8-2001

Level of Access

Open-Access Thesis

Degree Name

Master of Science (MS)

Department

Marine Science

Advisor

Sara M. Lindsay

Second Committee Member

Peter A. Jumars

Third Committee Member

Paul D. Rawson

Abstract

Deposit feeding organisms live and feed in marine soft-sediment habitats. This sediment makes up a majority of the material ingested by deposit feeders and contains a variety of edible material that may constitute their principal nutrient source. However, the specific components that are assimilated by these organisms, and the strategies they employ to efficiently collect those components, remain unclear. Sensory interactions between an organism and its surrounding environment typically play an important role in helping the organism detect and locate potential food. Accordingly, chemical sensing by deposit feeders is most likely involved in feeding, yet few specifics about this role and its ecological implications are known. This study, a multi-disciplined investigation of chemoreception, focuses on putative chemosensory structures located on the palps of the deposit-feeding spionid polychaete Diplydora quadrilobata. Using behavioral studies, neurophysiological methods, and molecular biological techniques, this study examines the sensory capabilities of this deposit feeder and their potential role as a mediator of selective feeding. A series of behavioral assays tested for feeding responses to a selected number of potential cues that might be used to indicate food availability or quality. Two sets of glass beads, one with and one without covalently bound compounds such as single amino acids, mixtures of amino acids, and single simple sugars, were separately presented to an organism. The differences in observed responses were used to identify these compounds as stimulatory, inhibitory, or inactive. Stirnulatory cues identified in the behavioral studies were then used to label, in an activity-dependent manner, putative receptor neurons in the palps. Stimulatory cues were perfused over the palp in the presence of the cationic molecule agmatine. Agmatine can enter into stimulated receptor neurons via activated non-selective cation channels. Those cells containing agmatine are then stained using an anti-agmatine antibody followed by silver intensification. Four putative sensory cell types located in the palps were identified by comparing cell labeling in response to the perfusion of a mixture of amino acids in the presence of agmatine to controls of agmatine in the absence of stimuli. Two of these cells types appear to be mechanosensory in function, and two appear to be chemosensory in function. Finally, molecular biological techniques were employed in attempts at isolating gene sequences that code for chemoreceptor proteins. Using RNA isolated fiom two tissues, D. quadrilobata palps and tails, single-stranded complementary DNA was constructed and amplified via the polymerase chain reaction. Gene expression patterns in the two tissues were compared (i.e. differential display) in order to isolate genes differentially expressed in the palps with the goal of finding receptor gene sequences. These studies indicate that chemoreception is an important influence in particle selection by this organism, and similarly suggest that this influence is at least partially mediated via chemoreceptor structures of the palp.

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