Measurements of middle-ear function in the Mongolian gerbil, a specialized mammalian ear

The middle ear of the Mongolian gerbil is thought to be specialized so that it can hear the 3,000-Hz and lower sounds produced by approaching predators. Evidence in the literature suggests several specializations: (1) an effect of the large middle-ear air spaces in the gerbil is to increase the sensitivity of this ear to sounds of 3, 000 Hz and lower in frequency; (2) the combined action of the middle-ear cavity and the significant pars flaccida of the tympanic membrane in the gerbil ear reduces the sensitivity to sounds of frequencies below 500 Hz. This paper describes anatomical and functional measurements of stapes motion and suggests that the stiffness of the gerbil ossicular system also acts to reduce sensitivity to low-frequency sounds. The primary conclusion is that the frequency dependence of the gerbil middle ear is the result of the interaction of multiple factors, thereby complicating the relationship between single structural specializations and overall function.