Convergence vs. Specialization in the ear region of moles (mammalia)

Abstract

We investigated if and how the inner ear region undergoes similar adaptations in small, fossorial, insectivoran-grade mammals, and found a variety of inner ear phenotypes. In our sample, afrotherian moles (Chrysochloridae) and the marsupial Notoryctes differ from most other burrowing mammals in their relatively short radii of semicircular canal curvature; chrysochlorids and fossorial talpids share a relatively long interampullar width. Chrysochlorids are unique in showing a highly coiled cochlea with nearly four turns. Extensive cochlear coiling may reflect their greater ecological dependence on low frequency auditory cues compared to talpids, tenrecids, and the marsupial Notoryctes. Correspondingly, the lack of such extensive coiling in the inner ear of other fossorial species may indicate a greater reliance on other senses to enable their fossorial lifestyle, such as tactile sensation from vibrissae and Eimer's organs. The reliance of chrysochlorids on sound is evident in the high degree of coiling and in the diversity of its mallear types, and may help explain the lack of any semiaquatic members of that group. The simplest mallear types among chrysochlorids are not present in the basal-most members of that clade, but all extant chrysochlorids investigated to date exhibit extensive cochlear coiling. The chrysochlorid ear region thus exhibits mosaic evolution; our data suggest that extensive coiling evolved in chrysochlorids prior to and independently of diversification in middle ear ossicle size and shape.

Ear Structures of the Naked Mole-Rat, Heterocephalus glaber, and Its Relatives (Rodentia: Bathyergidae)

“…From Ekdale’s data, only the pangolin Manis and an extinct elephantimorph of uncertain identity have canals of similar proportions. Among subterranean mammals, data tabulated by Crumpton et al [82] show that certain golden moles and the marsupial mole Notoryctes can be added to that list, while the membranous semicircular canals of the spalacid mole-rat Spalax have similar dimensions to those of Fukomys [33]. ‘Short and fat’ canals have evidently evolved several times in parallel among subterranean mammals, although they are not found in all species.…”

Does the morphology of the ear of theChinese bamboo rat (Rhizomys sinensis) show “Subterranean” characteristics?

“…The inner ear of R. sinensis possesses some characteristics which are connected with low frequency hearing and subterranean way of life. A long and highly coiled cochlea (3.25 turns) is considered a trait which enhances low frequency sensitivity (Crumpton et al, ). A high number of cochlear coils is typical for species with prevalent subterranean activity (Müller et al, ; Burda et al, ; Burda, ) but also for caviomorphs with different hearing ecologies (Pye, ; Begall and Burda, ; Teudt and Richter, ).…”

The middle and inner ears of the Palaeogene golden mole Namachloris: A comparison with extant species

“…From mapping ossicular size onto available phylogenies, Asher et al () and Crumpton et al () suggested that the small ear ossicles found in golden moles such as Amblysomus might represent a derived morphology among crown‐group chrysochlorids. Huetia was found to be the basal‐most species of the group in one phylogenetic study (Bronner et al, ), so the size of its malleus is particularly significant.…”

“…However, Asher et al () noted that the golden mole taxa most frequently reconstructed as basal in their Bayesian analyses had ‘slightly enlarged’ ( Huetia ), elongated ( Chrysochloris , Cryptochloris ) or enlarged and globular ( Eremitalpa ) mallei. Asher et al () raised the possibility that small ossicles may, in fact, be derived among extant golden moles, a suggestion later echoed by Crumpton, Kardjilov, and Asher (), based on similar phylogenetic arguments.…”