Meeting Abstract

84.5  Friday, Jan. 6  Comparing Sensory Abilities: Olfactory Bulb Size and Olfactory Sensitivity in Phyllostomid Bats EITING, T*; SMITH, T; FORGER, N; DUMONT, E; UMass Amherst; Slippery Rock Univ; UMass Amherst; UMass Amherst

When comparing olfactory abilities across species, the relative size of the olfactory bulb (OB) is often used to represent olfactory sensitivity (ability to detect low concentrations of odors). Species with larger OBs for their brain (or body) size are thought to have greater sensitivity to odors. If this assumption is true, the size of the olfactory bulb can provide valuable insights into relative sensory abilities across species. However, using the relative size of the OB as a proxy for functional ability has potential pitfalls. OB size could be related to features that do not reflect olfactory sensitivity, such as the size of the neuronal cell bodies or the proportion of non-neuronal cells in the OB. In this study we examine whether OB size is a significant predictor of more direct measures of olfactory sensitivity. One such measure is the “convergence ratio,” which is the ratio of the number of olfactory sensory neurons to the number of mitral cells with which they synapse. Higher convergence yields a greater chance of transmitting an action potential. Using 14 species of phyllostomid bats that represent a wide range of trophic adaptations, we test the hypothesis that relative size of the OB is a fair proxy for olfactory sensitivity. We predict a significant, positive relationship between relative OB size and the ratio of olfactory sensory neurons to mitral cells. Initial results based on cell counts derived from histological preparations support our hypothesis: relative OB volume is positively related to the olfactory convergence ratio. This finding supports the use of relative OB volume as a proxy for olfactory sensitivity in comparative studies.