Ultrasonic frogs can tune their ears to different sound frequencies

July 23rd, 2008 - 1:21 pm ICT by ANI  

Washington, July 23 (ANI): Researchers have discovered that a frog that lives near noisy springs in central China can tune its ears to different sound frequencies, much like the tuner on a radio can shift from one frequency to another.
It is the only known example of an animal that can actively select what frequencies it hears, according to the researchers.

The findings were made by scientists from the University of Illinois and the University of California at Los Angeles, as well as from the Chinese Academy of Sciences and the Massachusetts Eye and Ear Infirmary (at Harvard Medical School).

The discovery was made when researchers examined the eardrums of an unusual frog, Odorrana tormota, which communicates by making birdlike calls in the audible and ultrasonic frequency ranges.

Previous research by two of the authors showed that the frog produces and responds to ultrasonic calls.

In the new study, they sought to determine whether the frogs eardrums actually vibrate in response to these ultra high frequency sounds.

Using a laser vibrometer to measure the eardrums vibration, the researchers found that the eardrum did respond to sounds in the sonic and ultrasonic ranges.

But they also saw something they couldnt explain: The eardrums sensitivity to ultrasound sometimes disappeared altogether.

Normally sound waves strike the eardrum and if they are powerful enough and in a frequency range that the animal can perceive cause the eardrum to vibrate.

In most studies of frogs, the eardrum responds exactly the same way to the same sound stimulus. Even the eardrums of a dead frog will respond with unchanging predictability.

Past research showed that a frogs eardrum never responds differently to the same sound stimulus, said team leader Albert Feng, a professor of molecular and integrative physiology at Illinois.

Odorrana tormota is the only animal that is known to actively select what frequencies it hears. Researchers believe its unusual ears and ultrasonic calls are an adaptation to a noisy environment.

This was contrary to everything that we knew about its auditory system, said Feng.

O. tormota, the concave-eared torrent frog, is unusual in other ways.

Most frogs have ears on the body surface, but the torrent frogs ears are recessed.

Feng and his colleagues previously reported that O. tormota communicates in a noisy environment by emitting high frequency calls that include ultrasonic sounds, and can localize sound with astonishing precision.

Upon hearing a female call, a male will leap directly toward the sound with an error of less than 1 percent, a feat previously unheard of in frogs. (ANI)

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