Ecomorphological correlates of inner and middle ear anatomy within phyllostomid bats

Echolocation is the primary sense used by most bats to navigate their environment. However, the influence of echolocating behaviors upon the morphology of the auditory apparatus remains largely uninvestigated. While it is known that middle ear ossicle size scales positively with body mass across mammals, and that peak call frequency scales negatively with body mass among bats, there are still large gaps in our understanding of the degree to which allometry or ecology influences the morphology of the chiropteran auditory apparatus. To investigate this, we used mu CT datasets to quantify three morphological components of the inner and middle ear: ossicle size, ossicle shape, and cochlear spirality. These data were collected across 27 phyllostomid species, spanning a broad range of body sizes, habitats, and dietary categories, and the relationships between these variables and ear morphology were assessed using a comparative phylogenetic approach. Ossicle size consistently scaled with strong negative allometry relative to body mass. Cochlear spirality was significantly (p = .025) associated with wing aspect ratio (a proxy for habitat use) but was not associated with body mass. From a morphological perspective, the malleus and incus exhibited some variation in kind with diet and call frequency, while stapes morphology is more closely tied to body size. Future work will assess these relationships within other chiropteran lineages, and investigate potential morphological differences in the middle and inner ear of echolocating-vs-non-echolocating taxa.

Automated summary

Echolocation is the primary sense used by bats for navigation, but its influence on the morphology of the auditory apparatus is not well understood. This study used mu CT datasets to investigate the relationships between body size, habitat use, diet, and the morphology of the inner and middle ear in 27 bat species. The results showed that ossicle size scaled negatively with body mass, and cochlear spirality was associated with wing aspect ratio. Malleus and incus morphology varied with diet and call frequency, while stapes morphology was more closely tied to body size. Future research will explore these relationships in other bat lineages and compare echolocating and non-echolocating taxa.