Functional microanatomy of nasal turbinals in bats

Nasal turbinals are scrolled or folded internal nasal bones. In bats, prior work suggests turbinal anatomy is simplified in association with laryngeal echolocation (especially nasal emitting bats) and in association with insectivory. Using histology and iodine-enhanced micro-computed tomography, we examined a sample of 83 adult bats (54 species) to test these hypotheses more broadly across Chiroptera. Compared to bats that lack the capacity for laryngeal echolocation (i.e., Pteropodidae), all echolocating bats lack some of the more peripheral turbinals (e.g., interturbinals), and many lack at least one ethmoturbinal. Generally, turbinals are simple and plate-like in echolocating bats; most lack the scrolled turbinal morphology seen in pteropodids. When ethmoturbinals are measured in summed cross-sectional perimeters, pteropodids exhibit greater complexity in the olfactory recess compared to all echolocators. In contrast, some echolocators lack any olfactory recess. Bats that emit calls through the nasal cavity have novel turbinal morphology that could play a role in modifying calls. A preliminary quantitative survey suggests frugivores have greater olfactory surface area than other dietary groups, with as much as 66% of the nasal cavity lined with olfactory mucosa in the frugivorous pteropodid Cynopterus sphinx. Also, frugivorous bats within Phyllostomidae possess more elaborate turbinals than species belonging to other dietary groups in the family, including greatly enlarged interturbinals in the frugivorous Artibeus jamaicensis. Nevertheless, olfactory reduction (e.g., olfactory recess absence) is not universally seen among insectivores. Our results emphasize the multifunctionality of turbinals and suggest the evolution of differential growth rates and novel functions of the nasal cavity in extant bats.