Hearing loss in naked mole-rats is an advantage, not a hardship

Date:
September 3, 2020
Source:
University of Illinois at Chicago
Summary:
With six mutations in genes associated with hearing, naked mole-rats
can barely hear the constant squeaking they use to communicate with
one another. This hearing loss, which is strange for such social,
vocal animals, is an adaptive, beneficial trait, according to
new findings.



FULL STORY ==========================================================================
If naked mole-rats were human, they would be prescribed hearing aids. With
six mutations in genes associated with hearing, naked mole-rats can
barely hear the constant squeaking they use to communicate with one
another. This hearing loss, which is strange for such social, vocal
animals, is an adaptive, beneficial trait, according to new findings
published in the journal Current Biology.


========================================================================== Naked mole-rats are East African hairless mammals that are bald and
wrinkly with buck teeth. They live in underground colonies and their
social structure resembles that of bees -- there are soldiers, workers
and a queen. A lot of cooperation is required for a mole-rat colony to function. Naked mole-rats need to decide where to dig, how to defend the colony, and how to convey the location of food sources, and much of this
is accomplished by vocal communication.

"Naked mole-rats are constantly chirping and squeaking," said Thomas Park, professor of biological sciences and neuroscience at the University of
Illinois Chicago and one of the lead authors on the paper.

Park has been studying naked mole-rats for decades and has described some
of their odd traits, such as their ability to thrive under conditions
of low oxygen underground and their high tolerance for pain.

"We were curious about their hearing since they are so vocal, but research
had suggested that their hearing is actually quite bad," Park said.

Park and colleagues tested the hearing of mole-rats using technology
similar to that used for testing human hearing. They performed an auditory brain stem response test, during which electrodes placed on the scalp
pick up signals indicative of sound being processed in the brain. The researchers found the signals were weak, confirming naked mole-rats
have poor hearing. In fact, "their hearing is so bad that they would be candidates for hearing aids if they were people," Park said.



==========================================================================
Once the hearing loss was confirmed, Park and colleagues turned to the
mole- rats' genetics and found six mutations in genes associated with
hearing loss in humans.

"The fact that there were so many of these mutations strongly suggests
that these mutations were selected for because they are adaptive in some
way," Park explained.

The researchers also found the naked mole-rats lacked cochlear
amplification, a process by which specialized cells in the inner
ear help amplify sound signals before those signals are sent to the
brain. Cochlear amplification is aided by cells called outer hair cells,
which are located in the inner ear. Without proper functioning of these
cells, sounds are severely dampened.

"If the naked mole-rats didn't have these mutations, the constant noise
they produce could actually kill the hair cells responsible for hearing,"
Park said.

Hair cells receive auditory vibrations and send signals to the brain
where they are interpreted as sound. Really loud sounds actually kill
hair cells, which, unlike other types of cells, can't regenerate. Park
said this is why hearing loss in most mammals is progressive.

"Because the naked mole-rats lack functional cochlear amplification,
the sounds they hear don't ever get up to a level where they are lethal
to hair cells, and so the naked mole-rats can withstand this constant
cacophony without going totally deaf," Park said. "They are the only
mammals we know of that lack cochlear amplification." The new findings
suggest that mole rats may be a good animal model to investigate hearing
loss in humans.


========================================================================== Story Source: Materials provided by
University_of_Illinois_at_Chicago. Note: Content may be edited for style
and length.


========================================================================== Journal Reference:
1. Sonja J. Pyott, Marcel van Tuinen, Laurel A. Screven, Katrina
M. Schrode,
Jun-Ping Bai, Catherine M. Barone, Steven D. Price, Anna
Lysakowski, Maxwell Sanderford, Sudhir Kumar, Joseph Santos-Sacchi,
Amanda M. Lauer, Thomas J. Park. Functional, Morphological,
and Evolutionary Characterization of Hearing in Subterranean,
Eusocial African Mole-Rats.

Current Biology, 2020; DOI: 10.1016/j.cub.2020.08.035 ==========================================================================

Link to news story: https://www.sciencedaily.com/releases/2020/09/200903145006.htm

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