Gardiner’s frogs don’t have a middle ear or ear, but that doesn’t stop these little guys from being able to hear and croak!
You would think that not having ears means you wouldn’t be able to hear, but that’s not the case for this tiny frog species. Although scientists have previously believed the peculiar croakers were deaf, they have discovered that the amphibians are able to use their mouth cavities to pick up noise instead.
Gardiner’s frogs are one of the smallest frog species in the world, growing to only one centimetre long—about the size of a thumb tack. Scientists first discovered them in the islands of Seychelles, and didn’t know how the frogs were able to hear and make croaking sounds without the parts of the ear necessary to hear.
The auditory systems of frogs, and most four-legged animals, are mainly the same. Most have an outer ear (that helps collect sound waves and move them to the eardrum), a middle ear (the eardrum and tiny bones that amplify the sound waves and pass them on to the inner ear) and an inner ear (that translates the sound waves into electrical signals to our brain). Some animals can get by with just the middle and inner ear. However, with only an inner ear, an animal would only be able to hear less than one per cent of sounds, because the rest of the sound waves would never reach the inner ear.
The Gardiner’s frog seems to do this just fine, so a team of scientists led by Renaud Boistel, of France’s National Center for Scientific Research (CNRS), decided to find out how. By using X-ray imaging, the scientists found that the frog’s mouth acts as a replacement for both the outer and the middle ear. It amplifies the sound waves these frogs make when they croak, and sends them through thin layers of tissue at the back of the mouth to the inner ear.
“The combination of a mouth cavity and bone conduction allows Gardiner’s frogs to perceive sound effectively without use of a tympanic middle ear,” Boistel explains.
This shows that you don’t necessarily need a middle ear to be able to hear sounds. This information is helping scientists further discover how some creatures, including frogs and turtles, evolved the ability to hear.
The auditory system is what enables you to hear. It is made up of the outer ear, the middle ear and the inner ear. These parts are in charge of collecting sounds, processing them and then sending sound signals to your brain.