Sunday, October 4, 2009

Frog's Ears Can Switch Frequencies

Odorrana tormota is one of only two frog species known to have a concave ear. Researchers believe that its unusual ear structure and high-pitched calls are an evolutionary adaptation to a noisy environment. Photo courtesy of Albert S. Feng, University of Illinois.

Last frog blog for awhile. This was just so interesting that I HAD to post it even though there have been a few frog blogs lately. Scientists have discovered a frog that has developed the art of selective hearing just like some humans have.

A rare Chinese frog has been found to have the unusual ability to shift its hearing from one frequency to another the better to selectively choose what it hears.

The frog, Odorrana tormota, is the only known animal in the world to be able to manipulate its hearing system to select particular frequencies with the exception of the human animal. According to scientists; however, we run a very poor second in a race of two. Our hearing system is very slow when compared with that of the frog; and, our ability to tune in or out with precision is also inferior to that of the frog. We definitely ended up being #2 in this race. Or from a different point of view - dead last.

The rare amphibian likely evolved its hearing talent out of necessity, since its environment is so noisy.

"Their calling sites are on the steep banks of a fast-flowing body of water -- the Tao Hua Creek (at Huangshan Hot Springs in central China)," Albert Feng told Discovery News.

Feng, a professor of molecular and integrative physiology at the University of Illinois at Urbana-Champaign, added that the site is particularly noisy after spring showers while pointing out that humans have a similar inability to hear well over heavy rains.

"We pretty much have to shout at one another," he said.

The frog doesn't shout, but it instead sings like a bird either in audible chirp-like frequencies or by emitting very high-pitched ultrasonic sounds. This is the first time a frog has been known to sing in rising and falling harmonies - all other known frog calls go up or down.

Feng and his team were curious as to how this amphibian could hear these different vocalizations. They decided to analyze the frogs’ hearing system which was made much easier than expected since it was discovered that the frogs’ ears are completely transparent. Talk about a natural window!

Using a laser to measure the eardrum’s vibration, the team noticed that the eardrum responded to both audible and ultrasonic sounds. Interestingly, the eardrum’s sensitivity to ultrasonic noise sometimes mysteriously disappeared.

Discovery News tells us:
“Further investigation determined the frog actively opens and closes two narrow channels known as the Eustachian tubes, which connect the pharynx (part of the neck and throat) to the left and right middle ears. When open, the tubes couple the frog's left and right ears, making them sensitive to audible sounds from all directions. When closed, their ability to pick up ultrasonic frequencies kicks in.

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

This frog also possesses recessed ears instead of ones located on the body’s surface which may give it its ability to localize sound with amazing precision. When a wooing female starts to sing, male frogs have been recorded leaping directly in her direction with over 99% accuracy. They miss the mark less than 1% of the time. This level of accuracy has never been recorded in any other species of frog.

"On the one hand, I am surprised that any frog can open and close the Eustachian tubes," Carl Gerhardt, professor of biological sciences at the University of Missouri, told Discovery News.

"But on the other hand, I am not too surprised that this frog does it because it is also the first to be shown to have ultrasonic hearing and calls with ultrasonic components."

Discovery News also tells us:
“The frog's unique hearing system is already being used as a model for "intelligent" hearing aids that can spatially separate sounds, process them the way that human brains do, and boost sound signals of interest, such as differentiating background noise from that of a desired conversation.”

Via Discovery News

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