The tiny Gardiner’s frog, one of the smallest frogs in the world, once believed to be deaf, actually hears sounds through its mouth, scientists have found.
It has been a mystery how the one-centimetre-long Gardiner’s frogs from the Seychelles islands, which do not possess a middle ear with an eardrum, can croak themselves and hear other frogs. An international team of scientists using X-rays has now established that these frogs are using their mouth cavity and tissue to transmit sound to their inner ears. Some animals notably most frogs, do not possess an outer ear like humans, but a middle ear with an eardrum located directly on the surface of the head. Incoming sound waves make the eardrum vibrate, and the eardrum delivers these vibrations using the ossicles to the inner ear where hair cells translate them into electric signals sent to the brain. It is not possible to detect sound in the brain without a middle ear because 99.9 per cent of a sound wave reaching an animal is reflected at the surface of its skin. “However, we know of frog species that croak like other frogs but do no have tympanic middle ears to listen to each other. This seems to be a contradiction,” said Renaud Boistel from the University of Poitiers and French National Centre for Scientific Research (CNRS).