Talk about being tuned in to your mate. Some unique Chinese frogs can pick out the sounds of their mates in a noisy environment using a newly discovered ability that’s similar to tuning in a radio.
LAS researchers have found that a species of torrent frog, Odorrana tormota, can select different sound frequencies in much the same way that a radio listener switches among the different bands to get the clearest signal when tuning in to radio stations that broadcast in multiple bands. The frogs’ built-in skill enables them to pick up a clean signal from their mate, even in the noisy environment around the fast-flowing streams of central China.
It is also the only known example of an animal that can actively select what frequencies it hears, says Albert Feng, University of Illinois professor of molecular and integrative physiology.
This research likely has implications for human health. Earlier research on the mechanics of frog hearing enabled Feng and his colleagues to design an intelligent hearing aid that boosts sound signals.
The O. tormota frog is unusual in many respects, Feng explains. Most frogs have ears on the body surface, but these frogs’ ears are recessed. In an earlier study, Feng and his colleagues also discovered that these frogs communicate with each other by making birdlike calls in the audible and ultrasonic frequency ranges.
What’s more, they can localize the sound produced by their mates with astonishing precision, he adds. Upon hearing a female call, a male will leap directly toward the sound with an error of less than one degree, a feat previously unheard of in frogs.
Feng’s team discovered the frog’s ability to tune in to certain frequencies while they were examining the creature’s eardrums. The eardrum of the O. tormota frog is transparent, giving researchers a unique window into its inner workings. While puzzling over their measurements of the eardrum’s vibrations, they noticed the sudden appearance and disappearance of a dark shadow on the eardrum, Feng says.
Further investigation revealed that the frogs were opening and closing their Eustachian tubes, the two narrow channels that connect either side of the pharynx to the left and right middle ear.
“We said, ‘Whoa! This is bizarre!’” Feng recalls. “In all textbooks on sound communication and hearing in frogs, it is plainly stated that the Eustachian tubes are permanently open!”
But not for these frogs. Feng’s team found that when the frogs’ Eustachian tubes were closed, their eardrums became very sensitive to high frequency and ultrasounds. Conversely, when the Eustachian tubes were open, the eardrums responded mostly to low frequency sounds.
The frogs appear to be able to tune in to specific sound frequencies at will.
“They can shift to high frequency and ultrasonic hearing when the low frequency background noise of rushing water is too intense for them to pick out the calls of mates or rivals,” he says.
