Date of Award

5-2-2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

First Advisor

Charles Derby - Chair

Second Advisor

Marc Weissburg

Third Advisor

Manfred Schmidt

Fourth Advisor

William Walthall

Fifth Advisor

Donald Edwards

Abstract

Odor signals mediate a variety of behaviors in animals across a diversity of taxa. Despite dramatic morphological differences between animals from different taxa, several important features of olfactory system organization and processing are similar across animals. Because of this similarity, a number of different organisms including mammals, insects, and decapod crustaceans serve as valuable model systems for understanding general principles of olfactory processing. As in other organisms, including both vertebrates and insects, the chemosensory system of decapod crustaceans is organized into multiple anatomically distinct neuronal pathways. The two main pathways (the aesthetasc/ olfactory lobe pathway and non-aesthetasc/ lateral antennular neuropil pathway) originate in different populations of antennular sensilla and project to different neuropils in the brain. The functional significance of this parallel organization is not well understood in crustaceans or in many other species. Although in some insect species the functions of parallel pathways are clearly delineated by the types of odors processed by each, functional differences between parallel pathways in other organisms are much less distinct. A critical step towards understanding the functional significance of the multiple chemosensory pathways is to identify the specific behaviors that are driven by each pathway. Using spiny lobsters and crayfish as model organisms, the importance of each pathway was examined in three different behavioral contexts: (1) orientation to a distant food odor, (2) shelter selection in response to conspecific chemical signals, and (3) determination of conspecific social status. In each study, selective ablations of specific populations of antennular sensilla were performed, and the behavior of ablated animals was compared to that of intact controls. Results show that either the aesthetasc or non-aesthetasc pathway is capable of driving orientation to food odors, suggesting functional redundancy between the pathways in this behavior. In contrast social odors are processed preferentially by the aesthetasc pathway rather than the non-aesthetasc pathway, suggesting a unique role for the aesthetasc pathway in this context. As in other organisms possessing multiple chemosensory pathways, the dual antennular pathways in crustaceans display both unique and overlapping functions depending on the chemicals examined, and the behavioral context in which the signal is presented.

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