Flexibility within the middle ears of vertebrates

Mason, Matthew J.; Farr, Matthew R. B.

doi:10.1017/s0022215112002496

Cited by 31 publications

(24 citation statements)

References 145 publications

(243 reference statements)

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“…It articulates with a tiny lenticular apophysis mounted on a weakly-developed long process of the incus (Fig 4A). Increased flexibility within the ossicular chain can result in reduced sound energy transmission at high frequencies [84]. …”

Section: Discussionmentioning

confidence: 99%

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

2016

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Although increasingly popular as a laboratory species, very little is known about the peripheral auditory system of the naked mole-rat, Heterocephalus glaber. In this study, middle and inner ears of naked mole-rats of a range of ages were examined using micro-computed tomography and dissection. The ears of five other bathyergid species (Bathyergus suillus, Cryptomys hottentotus, Fukomys micklemi, Georychus capensis and Heliophobius argenteocinereus) were examined for comparative purposes. The middle ears of bathyergids show features commonly found in other members of the Ctenohystrica rodent clade, including a fused malleus and incus, a synovial stapedio-vestibular articulation and the loss of the stapedius muscle. Heterocephalus deviates morphologically from the other bathyergids examined in that it has a more complex mastoid cavity structure, poorly-ossified processes of the malleus and incus, a ‘columelliform’ stapes and fewer cochlear turns. Bathyergids have semicircular canals with unusually wide diameters relative to their radii of curvature. How the lateral semicircular canal reaches the vestibule differs between species. Heterocephalus has much more limited high-frequency hearing than would be predicted from its small ear structures. The spongy bone forming its ossicular processes, the weak incudo-stapedial articulation, the columelliform stapes and (compared to other bathyergids) reduced cochlear coiling are all potentially degenerate features which might reflect a lack of selective pressure on its peripheral auditory system. Substantial intraspecific differences were found in certain middle and inner ear structures, which might also result from relaxed selective pressures. However, such interpretations must be treated with caution in the absence of experimental evidence.

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Section: Discussionmentioning

confidence: 99%

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

2016

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“…Jaculus species are saltatorial, and it is conceivable that their long pedicles might similarly confer protection, in this case from the impacts of jumping. Further discussion of the role of flexibility within the ossicular chain may be found in Mason & Farr (), and in the companion paper (Mason, ). It is interesting to note that Spalax also resembles Jaculus in lacking a tensor tympani muscle, but shares with Gerbillurus an unusually wide annular ligament (Mason et al.…”

Section: Discussionmentioning

confidence: 99%

Structure and function of the mammalian middle ear. I: Large middle ears in small desert mammals

Mason

2015

Journal of Anatomy

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Many species of small desert mammals are known to have expanded auditory bullae. The ears of gerbils and heteromyids have been well described, but much less is known about the middle ear anatomy of other desert mammals. In this study, the middle ears of three gerbils (Meriones, Desmodillus and Gerbillurus), two jerboas (Jaculus) and two sengis (elephant-shrews: Macroscelides and Elephantulus) were examined and compared, using micro-computed tomography and light microscopy. Middle ear cavity expansion has occurred in members of all three groups, apparently in association with an essentially 'freely mobile' ossicular morphology and the development of bony tubes for the middle ear arteries. Cavity expansion can occur in different ways, resulting in different subcavity patterns even between different species of gerbils. Having enlarged middle ear cavities aids low-frequency audition, and several adaptive advantages of low-frequency hearing to small desert mammals have been proposed. However, while Macroscelides was found here to have middle ear cavities so large that together they exceed brain volume, the bullae of Elephantulus are considerably smaller. Why middle ear cavities are enlarged in some desert species but not others remains unclear, but it may relate to microhabitat.

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“…We found the ear structures of Diplomesodon to be very similar to those of Crocidura and Sorex; such differences that did exist tended to separate Sorex from the other two. The apparent fusion of malleus and incus in Sorex is an unusual feature of shrews of this genus (Mason and Farr, 2013).…”

Section: Vibration Production and Ear Morphologymentioning

confidence: 97%

Vocal development during postnatal growth and ear morphology in a shrew that generates seismic vibrations, Diplomesodon pulchellum

Zaytseva

Volodin

Mason

et al. 2015

Behavioural Processes

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The ability of adult and subadult piebald shrews (Diplomesodon pulchellum) to produce 160Hz seismic waves is potentially reflected in their vocal ontogeny and ear morphology. In this study, the ontogeny of call variables and body traits was examined in 11 litters of piebald shrews, in two-day intervals from birth to 22 days (subadult), and ear structure was investigated in two specimens using micro-computed tomography (micro-CT). Across ages, the call fundamental frequency (f0) was stable in squeaks and clicks and increased steadily in screeches, representing an unusual, non-descending ontogenetic pathway of f0. The rate of the deep sinusoidal modulation (pulse rate) of screeches increased from 75Hz at 3-4 days to 138Hz at 21-22 days, probably relating to ontogenetic changes in contraction rates of the same muscles which are responsible for generating seismic vibrations. The ear reconstructions revealed that the morphologies of the middle and inner ears of the piebald shrew are very similar to those of the common shrew (Sorex araneus) and the lesser white-toothed shrew (Crocidura suaveolens), which are not known to produce seismic signals. These results suggest that piebald shrews use a mechanism other than hearing for perceiving seismic vibrations.

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Flexibility within the middle ears of vertebrates

Cited by 31 publications

References 145 publications

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

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

Structure and function of the mammalian middle ear. I: Large middle ears in small desert mammals

Vocal development during postnatal growth and ear morphology in a shrew that generates seismic vibrations, Diplomesodon pulchellum

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