Bats, whales and dolphins use it to communicate. Baby rodents call their
mothers with it and now a rare Chinese frog has shown it can hear and respond to
ultrasounds, scientists said on Wednesday.
The frog, Amolops tormotus, is the first non-mammalian species known to use
the ultra-high frequencies that humans cannot hear.
It comes in handy to be heard above the pounding waterfalls and streams in
the mountainous region of east-central China where Amolops tormotus, which is
known as the concave-eared torrent frog, lives.
"Nature has a way of evolving mechanisms to facilitate communication in very
adverse situations," said Professor Albert Feng of the University of Illinois at
Urbana-Champaign.
"One way is to shift the frequencies beyond the spectrum of the background
noise. Mammals such as bats, whales and dolphins do this, and use ultrasound for
their sonar system and communication."
But until now it was not known that some frogs were able to use ultrasound.
Kraig Adler, a biologist at Cornell University in New York, first noticed the
frog with no external eardrums while surveying amphibians in China. He told
Feng, an auditory neuroscientist who studies frogs and bats, about his find.
Feng and his colleagues conducted tests on the frogs to determine whether
they could hear and respond to ultrasounds.
"Now we are getting a better understanding of why their ear drums are
recessed," said Feng, who reported his findings in the journal Nature.
"Thin eardrums are needed for detection of ultrasound. Recessed ears shorten
the path between eardrums and the ear, enabling the transmission to the ears,"
he added in a statement.
Ultrasounds are high-pitched sounds of more than 20 kilohertz (kHz) frequency
-- much higher than the frequency most birds, reptiles and amphibians can
hear.