Gardiner's Frog Uses its Mouth as a Pathway to its Inner Ear to Hear Noise

A recent discovery regarding a tiny frog native to a small nation of islands off the coast of Africa suggests the amphibian can hear using its mouth, Live Science reported.

The Gardiner's frog, from the Republic of Seychelles, is one of the smallest frogs in the world and it does not have ears. Recent research shows the little amphibians do not have a conventional middle ear and eardrum and use their mouth cavities to hear noise.

The researchers used x-ray imaging to look into the frog's head and found they used the cavities in their mouth to send sound waves to their inner ear. Just like any frog, they communicate using their signature croaking sound.

"We know of frog species that croak like other frogs but do not have tympanic middle ears to listen to each other. This seems to be a contradiction," lead study researcher Renaud Boistel, of the French National Center for Scientific Research (CNRS) in Paris, France, said in a statement.

The researchers, of course, had to test whether or not the Gardiner frog used sound to communicate with others. The researchers set up loud speakers in the frog's natural habitat that would play various frog calls. Males responded to the calls, proving they could hear despite lacking a middle ear and eardrum.

"Whether body tissue will transport sound or not depends on its biomechanical properties," study co-author Peter Cloetens, a scientist at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, said in a statement. "With X-ray imaging techniques here at ESRF, we could establish that neither the pulmonary system nor the muscles of these frogs contribute significantly to the transmission of sound to the inner ears."

Other theories to how the frog could hear included extra auditory pathways through the lungs or other muscles, but the team still believed they must lead to the inner ear.

By studying the x-ray results, the scientists determined the mouth amplifies the sound, which is then transmitted to the inner ear via tissues and bones. The researchers published their study online Monday in the journal Proceedings of the National Academy of Sciences.