Nature

Weird Frog Hears Only Sounds It Wants

The ears of Odorrana tormota can detect certain sound frequencies

By Gabriel Gache, Science News Editor

23rd of July 2008, 10:29 GMT

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A frog living near the noisy springs in central China was found by researchers from the University of Illinois and the University of California to have the ability to tune its ears to hear only certain sound frequencies, as opposed to hearing all the sounds in the acoustic spectrum at the same time, as humans do. Previous studies have shown that this particular frog (Odorrana tormota) is able to communicate in both acoustic and ultrasonic frequencies.

Willing to understand how the eardrums of the frog respond to ultra-high frequency sounds, the research team set up a laser vibrometer to measure the eardrum's vibration in both sonic and ultrasonic ranges. To their surprise, the results showed that in certain conditions the eardrum becomes totally non-reactive to ultrasound.

Usually, when a powerful sound wave in the frequencies perceived by the animals' ears hits the eardrum, it causes it to vibrate, responding similarly every time and to the same stimuli. However, in the case of Odorrana tormota, the same sound can produce unpredictable responses. "This was contrary to everything that we knew about its auditory system," said Albert Feng, a professor of molecular and integrative physiology from the University of Illinois.

And the weird characteristics of this frog don't stop here. Unlike most frogs, which have their ears on the body surface, the ears of O. tormota are recessed. Additionally, the ear drums appear to be transparent, exhibiting the sudden appearance of a dark shadow in certain conditions. A closer examination showed that the Eustachian tubes of the frog are able to actively open and close.

"We said, 'Whoa! This is bizarre!' In all textbooks on sound communication and hearing in frogs, it is plainly stated that the Eustachian tubes are permanently open!" said Feng.

According to the results of the research, when the Eustachian tubes of the frog are open, the ears become connected to each other, giving it directional sensitivity and the ability to hear low frequency sounds and shift to high frequency and ultrasonic hearing only when the low frequency background noise becomes too high.

TAGS:

sound | ear | eardrum | Eustachian tubes | frequency

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