Date of Award

4-16-2008

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Donald. H. Edwards - Chair

Second Advisor

Ronald L. Calabrese

Third Advisor

Daniel Cattaert

Fourth Advisor

Paul. S. Katz

Abstract

Adaptation to changing social conditions is important for many social animals. Here, the effects of social experience on the behavior and neurophysiology of the red swamp crayfish, Procambarus clarkii, were studied. Evidence is presented that shows juvenile crayfish interact and form social order, and their behavior patterns shift in accordance to social status. Dominant animals maintain a high level of aggressive behavior, while subordinates shift their behavior pattern from aggressive to submissive behavior. Adult male crayfish show similar behavior pattern during dominance formation. However, this work demonstrates that male crayfish adopt a unique strategy to signify the formation of a social order expressed in the form of pseudocopulation. Pseudocopulation between male crayfish signifies the acceptance of the social status and leads to the reduction of aggression of dominants and enhances the survival of subordinate animals. I investigated the long-term effects of social status on the behavioral and physiological responses of crayfish to unexpected sensory touch. I discovered that animals of different social experience display different orienting responses that correlate with in vivo electromyographic recordings from the legs’ depressor muscle. The status-dependent response patterns observed in vivo are retained in a reduced, in vitro, preparation that lacks descending input from the brain. The role of serotonin (5-HT) was investigated in mediating the motor output patterns of the depressor nerve. Putative serotonergic innervations of the depressor nerve were identified that originate from serotonergic neurons located in the first abdominal ganglion. Selective stimulation of the ipsilateral 5-HT neuron enhances the response of the depressor nerve to sensory stimulation. Application of 5-HT modestly increased the tonic firing activity of the depressor nerve in social isolates and subordinates but significantly decreased the activity in dominants. This work illustrates that the formation of a dominance relationship significantly and immediately alters the behavior of the participants. As the social relationship matures, the social experience that develops affects the underlying neurophysiology that mediates the behavior. It will be of great interest in future studies to identify not only the effects rather the mechanisms of how social experience induces physiological changes.

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Biology Commons

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