Frogs use their lungs to drown out the mating calls of other species

March 4 (UPI) -- Frog lungs work kind of like noise cancelling headphones, according to a new study, helping females drown out the overwhelming cacophony of competing mating calls.

The new findings, published Thursday in the journal Current Biology, help explain how females are able to home in on the songs of individual male frogs.

Mating songs help female frogs select fit males to copulate and reproduce with, but because the mating season of myriad frog species overlap, on the banks of a small pond or in the thick of a secluded tree stand, the songs of dozens of frog species can fill the air.

Even if a pond or section of forest is only occupied by a single species, a dozen mating songs sung simultaneously can prove disorienting.

To cope, females utilize their lungs.

"In essence, the lungs cancel the eardrum's response to noise, particularly some of the noise encountered in a cacophonous breeding 'chorus,' where the males of multiple other species also call simultaneously," lead author Norman Lee, assistant professor of biology at St. Olaf College in Minnesota, said in a press release.

Previous studies have highlighted an important vocal pathway in frogs, linking the amphibians' air-filled lungs with air-filled middle ears via the glottis, mouth cavity, and Eustachian tubes. Scientists previously estimated the pathway might help frogs aim their vocalizations.

For the new study, researchers focused on the effects of inflated lungs on vocal vibrations in green tree frogs.

Scientists used laser vibrometry to measure the resonance of the lungs in response to different frequencies. The analysis showed inflated lungs dampen certain frequencies, allowing others to be more easily perceived.

"This is analogous to signal-processing algorithms for spectral contrast enhancement implemented in some hearing aids and cochlear implants," said senior author Mark Bee, professor of ecology, evolution and behavior at the University of Minnesota-Twin Cities.

"In humans, these algorithms are designed to amplify or 'boost' the frequencies present in speech sounds, attenuate or 'filter out' frequencies present between those in speech sounds, or both. In frogs, the lungs appear to attenuate frequencies occurring between those present in male mating calls. We believe the physical mechanism by which this occurs is similar in principle to how noise-canceling headphones work," Bee said.

After measuring the vibrational qualities of inflated lungs, researchers developed a physiological model to better understand how the lungs' frequency-dampening abilities influence the absorption of sound inside the inner ears of green tree frogs.

Scientists hypothesized the inner ears of frogs have evolved to pick up the calls of their own species, and the latest simulations showed the lungs likely enhance this tuning ability.

"An ancient adaptation for detecting sound via the lungs has been evolutionarily co-opted to create auditory contrast enhancement that contributes to solving a multi-species cocktail party problem," researchers wrote in their paper.