Naked mole rats have poor hearing because, unlike other mammals, they have abnormal outer hair cells that can’t amplify sound. The animals could be used to model human deafness and help develop treatments.
A Dutch research team first measured the animals’ neural responses to various tones played to them. This confirmed that they struggled to hear quiet sounds and could only perceive sound between a narrow frequency, between 0.5 and 4 kHz. Humans, by contrast, can detects sounds between about 0.02 and 20 kHz. The researchers then recorded the sound transmitted by the cochlea, a part of the inner ear typically shows the ear is amplifying sound information. They found that no such amplification occurred in either species of mole rat.
The team used a scanning electron microscope to look more closely at the outer hair cells of the mole rats’ ears. The hair cell bundles in a particular section of the ear were found to be abnormal compared with those of other rodents, like mice and gerbils.
Results of their research indicates that the mole rats evolved to have poor hearing sensitivity.
Although the group is unsure why they evolved to have poor hearing, there are a couple of hypotheses. One is that the creatures lost some of their hearing ability because the sense isn’t required underground. Another possibility is there are a lot of echoes underground, so the mole rats evolved to have poor hearing to avoid acoustic overexposure.
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*featured image courtesy wikimedia commons
