To determine that Gardiner's frogs do, in fact, use sound to communicate with one another, the scientists set up loudspeakers in the natural rain forests of Seychelles and played pre-recorded frog songs. Males in the rain forests promptly answered the songs, signifying they could hear the recording, the researchers said.
Several ideas had been suggested for how the Gardiner's frogs could hear sounds, including extra auditory pathways through the lungs or special muscles in the frogs that connect to the inner ear.
"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."
By studying X-ray images and numerical simulations, the researchers discovered that Gardiner's frogs receive sound through their heads. The mouth amplifies the frequencies and the sound is transmitted through tissue and bones in the skull to the inner ear.