Date of Award

5-2005

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Science (MS)

Department

Marine Biology

Advisor

Sara M. Lindsay

Second Committee Member

J. Malcolm Shick

Third Committee Member

Seth Tyler

Abstract

Bioturbation, the mixing and movement of sediment particles by animals shapes the chemistry, physical structure, and ecology of benthic marine habitats. For example, the feeding behavior of spionid polychaetes affects sediment chemistry and benthic community ecology as the tube-building marine worms forage with a pair of feeding tentacles (palps). This study investigates the neural mechanisms that underlie deposit feeding by spionid polychaetes. Ciliated cells on the palps, the organization of the nervous system in general, and the distribution of the neurotransmitters serotonin (5-HT) and FMRF-amide were compared in Dipolydora quadrilobata and Pygospio elegans. The distribution of serotonin was also examined in Polydora cornuta and Streblospio benedicti. Immunohistochemistry and fluorescence (confocal laser scanning) microscopy were used to label and image sensory cells and nerves. The possible sensory nature of ciliated cells found on spionid palps was also investigated using these techniques. In addition to labeling the nervous system in general, antibodies directed against acetylated a-tubulin, a component of the microtubules in cilia and neurons, specifically showed the innervation of ciliated cells in the palps of each species. Distributions of serotonin (5-HT) and FMRFamide were also examined. Serotonin immunoreactivity revealed (1) cells underlying the food groove of the palps, (2) palp nerves and their connections with the cerebral ganglion (brain), and (3) segmental patterns of nerves in the ventral nerve cord (VNC). FMRFamide immunoreactivity revealed ( 1 ) the general nervous system, including rnetamerically repeated units of cell bodies (perikarya) in the VNC, (2) palp nerves and cerebral ganglia structure, and (3) perikarya of ciliated cells on the palps. Serotonin modulates various behaviors in many animals. During an experiment examining the effects of serotonin on the feeding behavior of the spionid polychaete, Streblospio benedicti, I observed unexpected increases in the number of spontaneous escape responses. Like other spionids, S. benedicti inhabits tubes in sediment and will immediately withdraw (escape) into its tubes when a threat is perceived (e.g., a disturbance or shadow over the tube). The effect of 5-HT on the frequency of S. benedicti escape was measured by comparing the number of 5-HT-induced tubewithdrawals to those in seawater controls. Significantly more withdrawals occurred under the influence of 5-HT; a 10 pM solution was enough to elicit the escape response. Confocal laser scanning microscopy was used to image the serotonergic nervous system and musculature in S. benedicti. Serotonin immunoreactivity in the ventral nerve cord of the worm reveals large axons which may mediate the escape response by controlling muscular contractions. Results of this experiment support the idea that serotonin influences a natural predator avoidance behavior in this spionid polychaete.

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