Measurements of middle-ear function in the Mongolian gerbil, a specializedmammalian 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 predator s. Evidence in the literature suggests several specializations: (1) an effe ct of the large middle-ear air spaces in the gerbil is to increase the sens itivity of this ear to sounds of 3,000 Hz and lower in frequency; (2) the c ombined action of the middle-ear cavity and the significant pars flaccida o f the tympanic membrane in the gerbil ear reduces the sensitivity to sounds of frequencies below 500 Hz. This paper describes anatomical and functiona l measurements of stapes motion and suggests that the stiffness of the gerb il bil ossicular system a Iso acts to reduce sensitivity to low-frequency s ounds. The primary conclusion is that the frequency dependence of the gerbi l middle ear is the result of the interaction of multiple factors, thereby complicating the relationship between single structural specializations and overall function.