This ear-like frog has lungs that block out noise, research shows

To succeed in breeding, many male frogs sit in one place and call to their intended mates. But this raises an important question that is familiar to anyone trying to listen to someone talk at a busy cocktail party: how does a woman hear and then find a male choice of her gender itself among all the inappropriate back sounds, including the sound of other frog species. ? Now, researchers report March 4 in the journal Conventional biology have been found to do so thanks to a set of lungs which, when tightened, reduce the sensitivity of the eardrum to environmental noise in a given frequency range, making it easier to zero into the calls of the companion.

“In fact, the lungs suppress the eardrum’s response to sound, especially some of the sound found in a ‘cacophonous breeding chorus,’ where other heterosexual males call at the same time,” says lead author Norman Lee of St. Olaf’s College in Minnesota.

The researchers explain that their lungs are called “increased spectral divergence”. That’s because it makes the frequencies in the male call spectrum stand out compared to noise at nearby frequencies.

“This is similar to signal processing algorithms for spectral contrast enhancement implemented in some hearing aids and cochlear implants,” says lead author Mark Bee of the University of Minnesota-Twin Cities. “In humans, these algorithms are designed to amplify or‘ increase ’the frequencies present in speech sounds, to reduce or filter out the‘ frequency ’of the speech. present between those in speech sounds, or both.In frogs, the lungs appear to reduce the frequency of occurrences between the ones.is present in male mating calls.We believe that the physical equipment by which this happens is similar in principle to the way in which headphones stop working sound. “

Scientists have long known that vocal signals are essential in reproduction in most frogs. In fact, frogs have a specific sound pathway that can send sounds from their air-filled lungs to the air-filled middle ears through the glottis, mouthpiece, and Eustachian tubes. But the very role of the lung-sounding transmission to this ear was a puzzle. Earlier studies suggested that the frog’s lungs may play a role in increasing the degree of direction-dependent eardrum vibrations, thus improving the ability of male audiences to detect sexual advertisements. . But Bee’s team has found out that wasn’t true.

Further analysis of the data suggested a different explanation: although the state of lung inflation had no effect on directional hearing, the sensitivity of the eardrum was significantly affected. With inflated lungs, the eardrum vibrates less in response to sounds in a specific frequency range. They took them to a new idea: that the lungs were damaging vibrations, thus making a noise.

In fact, their studies using laser vibrometry have shown that selectively inflated lung repositioning reduces the sensitivity of the eardrum to frequencies between the two celestial peaks present in the calls of frogs of the same sex. He confirmed that a woman can hear men of her own sex no matter the degree of inflation of her lungs. Thus, the lungs had no effect on the “symptoms” in which a woman is interested. But what about the “sound”?

They already knew that the main sound source for a particular species of frog is the calls of other species of frogs that breed at the same time and call in the same choruses. However, they did not know how many or what other species might be “converging” in a series of mixed species with green trees throughout their geographical range, much less as was the frequency spectrum. their calls watching. To find out, they turned to publicly available data from a citizen science project called the North American Amphibian Study Program. Their analysis of these data reveals that the inflated lungs of the green tree would make it more difficult to hear the calls of other species while leaving their ability to hear the calls of their own species intact.

“Needless to say, we think this result – frog lungs suppressing the eardrum’s response to a sound created by other species of frogs – is pretty cool!” Bee says.

Finally, they created a physiological model of sound processing with an inner ear of the green tree to study how the impact of the lungs on the eardrum could translate into stronger cloud responses to the calls of their own species. They think it works like this: the inner ear is, in some ways, “tuned” to better respond to the frequencies in the calls of the species itself. But that tuning is not perfect. The authors suggest that the primary function of the lungs in hearing is to tune or develop this tuning, allowing the inner ear to generate stronger cloud responses to the calls of the sex. itself by reducing the cloud responses that are driven by the calls of other species.

The findings show the power of evolution to co-opt existing changes for new activities, the researchers say. In future work, they want to find out more about the physical interactions between the three sources of sound (external, internal through the opposite ear, and internal through the lungs). which determines the vibration response of the eardrum. They also want to know more about the extent of noise abatement in frogs.

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This work was supported by the U.S. National Science Foundation.

Conventional biology, Lee et al .: “Increased lung-mediated comparison improves the signal-to-noise ratio for communication in frogs”
https://www.cell.com/current-biology/fulltext/S0960-9822(21)00113-5

Conventional biology (@CurrentBiology), published by Cell Press, is a bi-monthly journal of papers across all fields of biology. Conventional biology seeks to encourage communication across the fields of biology, both by publishing important findings of common interest and through a face-to-face topic accessible to non-experts. Visit http: // www.cells.com /conventional biology. To receive Cell Press media alerts, contact [email protected].