Neuronal scaling in the olfactory system of bats.

Abstract

Comparative studies are a common way to address large-scale questions in sensory biology. For studies that investigate olfactory abilities, the most commonly used metric is olfactory bulb size. However, recent work has called into question the broad-scale use of olfactory bulb size. In this paper, we use three neuroanatomical measures with a more mechanistic link to olfactory function (number of olfactory sensory neurons (OSNs), number of mitral cells (MCs), and number of glomeruli) to ask how species with different diets may differ with respect to olfactory ability. We use phyllostomid bats as our study system because behavioral and physiological work has shown that fruit- and nectar-feeding phyllostomids rely on odors for detecting, localizing, and assessing potential foods, while insect-eating species do not. Therefore, we predicted that fruit- and nectar-feeding bats would have larger numbers of these three neuroanatomical measures than insect-eating species. In general, our results supported the predictions. We found that fruit-eaters had greater numbers of OSNs and glomeruli than insect-eaters, but we found no difference between groups in number of MCs. We also examined the allometric relationship between the three neuroanatomical variables and olfactory bulb volume, and we found isometry in all cases. These findings lend support to the notion that neuroanatomical measures can offer valuable insights into comparative olfactory abilities, and suggest that the size of the olfactory bulb may be an informative parameter to use at the whole-organism level.