Middle ear pneumatization in nonhuman primates: a comparative analysis.

17 pagesInternational audienceObjectives: We test the effects of body mass and phylogeny on middle ear cavitypneumatization, and the role of pneumatization in hearing function, spanning theanatomical, ecological, and behavioral diversity of nonhuman primates.Materials and methods: All cavities were segmented in middle ear scans of 96 specimens,from 12 strepsirrhine and 15 haplorhine extant species. We measured the tympaniccavity (TC) separately, and all other middle ear spaces together (MES), calculatingthe degree of pneumatization with the surface area-to-volume ratio. We tested bodymass effect with linear regression; we evaluated the phylogenetic signal and selection patterns,using a Kappa statistic test, and Ornstein-Uhlenbeck models (OU). We investigatedthe link between pneumatization and hearing sensitivity using phylogenetic regression.Results: Testing body mass reveals an allometric pattern for both TC and MES dimensions.Degree of pneumatization in MES is dependent on body mass in haplorhines:larger animals have more pneumatized MES. Differences at various taxonomic rankswere observed for MES, while no phylogenetic influence was observed for TC. Infraorderselection patterns are different. Auditory performance is significantly related todegree of pneumatization, indicating that a pneumatized middle ear is associated withbetter perception of low frequencies.Discussion: Pneumatization in MES is under differential selective pressure, indicatingseveral optima for this trait. Pneumatization in MES probably modifies hearing sensitivitythrough pressure regulation mechanisms, auditory bulla size reduction, and frequencymodulation. This could explain strepsirrhine adaptation to high-frequencyperception, while haplorhine auditory perception is adapted to a broader soundrange, including high and low frequencies