Date of Award

5-26-2006

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Donald H. Edwards - Chair

Second Advisor

Manfred Schmidt

Third Advisor

Charles D. Derby

Fourth Advisor

Deborah J. Baro

Abstract

Crayfish (Procambarus clarkii) form dominance hierarchies, which are patterns of repeated fights with expected outcomes of winner and loser. Establishment of hierarchies allows dominants the first access to limited resources over subordinates, and leads to behavioral and cellular changes corresponding to the social status. Here, the animals¡¯ responses to an unexpected unilateral touch, a non-social stimulus, were examined with respect to their social status and to their social context. Isolates oriented to the stimulus source with raised claws and elevated posture. Dominants also oriented to the stimulus both when tested alone and in the presence of a subordinate. Subordinates oriented to the stimulus while separated from their familiar dominant partner; however, they avoided it when tested while paired with the dominant. In subsequent tests first while semi-separated from the dominant and later while fully separated, the same subordinates displayed more orienting responses as the duration of post-fight separation increased. These results suggest that the lingering effects of recent social experience influence the behavior of subordinate animals. During fights, crayfish release urine toward each other, providing critical chemosensory cues for establishing hierarchies. Throughout the lifespan, new neuronal precursors are added into clusters of olfactory local and projection interneurons (clusters 9 and 10). Here, the effect of pair-wise social experience on neurogenesis in these brain regions was examined using the proliferation marker bromodeoxyuridine. Groups of proliferating cells in clusters 9 and 10 formed distinctive comma shapes. The BrdU-positive nuclei in the head part of the comma were smaller and more circular than those in the tail part of the comma. Subordinates had fewer new neuronal precursors surviving in cluster 9 after 14 days than did dominants. Mitotic activity was not influenced by social status. The effect of social experience on neurogenesis remained when the effect of body growth rate on neurogenesis was removed. In conclusion, social domination enhances cell survival compared to social subordination. Although the function of these surviving newborn neuronal precursors is unknown they may enhance the learning ability of dominant crayfish.

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