These animals suffer from hearing loss as they age, just like people
The Hearing loss is a hallmark of aging humans and most mammals, but until now it was thought not to affect bats, which depend on echolocation for survival; that is, of its ability to discern high frequencies. They are precisely the first to be lost with age. But a new study has come to show just the opposite.: Bats experience hearing loss in old age, and at the same rate as humans.
A group of Israeli researchers has tested the hearing of 47 Egyptian fruit bats (Rousettus aegyptiacus), 24 males and 23 females, all older than one year, through the recording your auditory response brainstem and cochlear microphonics, as well as cochlear histology in four of those bats. They monitored their brains’ electrical responses to sounds of different pitches and volumes.
After assessing the age of the animals, they discovered that they exhibited a clear age-related hearing loss, with much more prominent decay at the higher frequencies. The rate of deterioration was approximately one decibel per year, very similar to hearing loss seen in humans.
The authors verified that these bats are exposed to continuous immense noise, mainly from social vocalizations (they make frequent, loud social calls to each other), supporting the assumption that bats might be partially resistant to loud noise.
The results of the research, published in ‘Life Science Alliance’, have shown, contrary to what was previously assumed, that the bat is a model animal for the study of age-related hearing loss.
extremely noisy neighborhoods
The data collected also suggests that, since live in extremely noisy coloniesbats may have evolved some innate ability to limit age-associated hearing loss.
Many species of bats have a extremely long life expectancy of more than 40 yearscompared to other mammals of similar size, such as mice.
“Although the high frequency hearing confers a survival benefit to many animals, it is essential for the survival of echolocating bats, which depend on it to orient themselves in their environment,” explains Yossi Yovel, a neuroecologist at Tel Aviv University and co-author of the study.
Evidence suggests that, like humans, bats experience an age-related decline in the structure and function of their cochlea, as well as a decreased speed of auditory nerve processing.
This last symptom, known as neural presbycusiscan affect speech comprehension in humans and could make echolocation difficult for old bats.
“The fruit bats we studied rely on echolocation for several tasks, but they also rely heavily on vision,” says Yifat Tarnovsky, co-author of the study. “Therefore, it will be important to replicate our tests in bats with poor vision, where echolocation is almost the only orientation mechanism,” he says. That will be the team’s next challenge.
Tarnovsky and his colleagues placed several microphones inside the fruit bat cave and discovered that the animals are continuously exposed to more than 100 decibels of noise, roughly equivalent to the noise produced by a motorcycle or chainsaw.
“Surprisingly, however, the loudest sounds were produced at lower frequencies at which bats show little or no hearing loss in old age,” the study authors note.
early listening skills
“When taken together, the very high noise levels fruit bats are exposed to and the mild (human-like) levels of age-related hearing loss suggest that bats might have some special accommodations to cope with their very noisy environments,” says Yovel.
The researchers hope that understanding these adaptations may provide insight into the mechanisms of age-related hearing loss in humans.
The authors of this research have been studying Egyptian fruit bats for years. They have discovered, for example, that even newborns of the species are capable of directing echolocation waves.
“Just after birth, pups can also hear echolocation clicks produced by adults and can produce their own clicks,” they noted after a study they conducted two years ago.
They found that the pups make extremely short clicking calls in response to clicks and other sounds they heard. The researchers note that this demonstrates “early listening skills“.
They also verified that the newborns of this species are not only sensitive to adult sounds, but can imitate them. And that already 35 days after birth, coinciding with the beginning of the flight, the frequency and duration of the clicks change to coincide with those of adults.
https://www.life-science-alliance.org/content/6/6/e202201847
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