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Ear morphology in two root-rat species (genus Tachyoryctes) differing in the degree of fossoriality

Abstract

It is supposed that the subterranean lifestyle in mammals is reflected in ear morphology and tuning of hearing to low frequencies. We studied two root-rat species to see if their ear morphology reflects the difference in the amount of their surface activity. Whereas the more subterranean Tachyoryctes splendens possesses shorter pinnae as expected, it has smaller bullae compared to the more epigeic Tachyoryctes macrocephalus. The ratio between the eardrum and the stapedial footplate area and the ratio between the mallear and the incudal lever were lower in T. splendens (19.3 ± 0.3 and 1.9 ± 0.0, respectively) than in T. macrocephalus (21.8 ± 0.6 and 2.1 ± 0.1), probably reflecting the latter’s higher surface activity. The cochlea in both species has 3.5 coils, yet the basilar membrane is longer in the smaller T. splendens (13.0 ± 0.5 versus 11.4 ± 0.7 mm), which indicates its wider hearing range and/or higher sensitivity (to some frequencies). In both root-rat species, the highest density of outer hair cells (OHC) was in the apical part of the cochlea, while the highest density of inner hair cells (IHC) was in its middle part. This OHC density pattern corresponds with good low-frequency hearing, whereas the IHC pattern suggests sensitivity to higher frequencies.

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The data that support the findings of this study are available within the article.

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Abbreviations

BH:

Bullar height

BL:

Bullar length

BM:

Basilar membrane

BV:

Bullar volume

BW:

Bullar width

CBL:

Condylobasal length

IHC:

Inner hair cells

OC:

Organ of Corti

OCW:

Organ of Corti width

OHC:

Outer hair cells

TR:

Triad = three rows of OHC

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Acknowledgements

We thank the Ethiopian Wildlife Conservation Authority (EWCA) for permission to conduct field research in Ethiopia. We thank the Bale Mountains National Park for kind cooperation. We thank Matěj Lövy, Tereza Vlasatá, and Jan Šklíba for assistance and collecting specimens of Tachyoryctes macrocephalus in the field and to Christopher Mark Steer for English proofreading.

Funding

This work was supported by the Czech Science Foundation (GAČR) projects P506/11/1512 and 20-10222S.

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Correspondence to Lucie Pleštilová.

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All procedures involving wild-caught animals were performed and approved by the Institutional Animal Care and Use Committee at the University of South Bohemia and the Ministry of Education, Youth and Sports (n. 7942/2010-30).

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Pleštilová, L., Hrouzková, E., Burda, H. et al. Ear morphology in two root-rat species (genus Tachyoryctes) differing in the degree of fossoriality. J Comp Physiol A 207, 469–478 (2021). https://doi.org/10.1007/s00359-021-01489-z

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Keywords

  • Ear morphology
  • Hearing
  • Subterranean mammals
  • Tachyoryctes
  • Spalacidae