Structure, function and context : the impact of morphometry and ecology on olfactory sensitivity

Abstract

In this thesis, the relationships of olfactory sensitivity to three biological variables were tested. The sensitivity of a marine mammal, the sea otter (Enhydra lutris) was measured in order to determine whether a marine lifestyle results in impaired olfaction. The effect of dietary relevance on sensitivity to specific odorants was evaluated. Finally, a new morphometric model of olfactory uptake efficiency was developed and tested against behavioral measurements of olfactory sensitivity in twelve mammalian species from five orders. Olfactory thresholds were obtained for the first time from two sea otters for seven odorant compounds from various natural sources. Otters were trained using operant conditioning to participate in direct behavioral testing. Sea otter olfactory sensitivity was comparable to that of previously studied terrestrial mammals. The incidence of an odorant in the diet of the olfactor was found to influence specific sensitivity to that compound but to varying degrees among different mammalian orders. Nasal cavity specimens were measured using radiologic (CT scan) and histologic (light microscopy) techniques. Surface areas and volumes of the nasal cavity were used to calculate the Olfactory Uptake Efficiency (OUE). OUE is significantly related to olfactory bulb volume. A possible relationship was found between OUE and general olfactory sensitivity.