A group of scientists from France and the Seychelles led by Renaud Boistel from the Centre national de la recherche scientifique (CNRS) and the University of Poitiers have solved the mystery of how Gardiner's tree frogs are able to hear and communicate by croaking like other frogs according to a report published in the Sept. 2, 2013, edition of the journal Proceedings of the National Academy of Sciences.
Gardiner's tree frog (Sooglossus gardineri) is only found in the Seychelles. The frog is on average about 11 millimeters in length making it one of the smallest in the world.
Unlike most frogs living today, Gardiner's tree frogs do not have an eardrum located directly on the surface of the head. This fact has puzzled biologists since the discovery of the frog. The question is how does the frog hear?
The researchers established that Gardiner's tree frogs can hear and communicate like other frogs by broadcasting frog croaks into areas where Gardiner's tree frogs live. The frogs responded by croaking back indicating the frogs can hear and communicate.
X-ray imaging of the Gardiner's tree frog head and mouth at the European Synchrotron Radiation Facility revealed that the frog’s mouth acts as an amplifier that directs sound to the middle ear at the back of the frog’s mouth. Hearing is not possible without an inner ear.
Gardiner's tree frog has existed in a closed environment for 47 to 65 million years. Over time the frog adapted to be able to hear and communicate by the minimization of the thickness of the layers of skin in the mouth that cover the inner ear allowing the transfer of sound waves more readily. The frog’s skin adapted to transfer almost 100 percent of an incoming sound wave to the inner ear.