|
The findings,
published in the March 16 issue of Nature, represent the first
documented case of an amphibian being able to communicate like bats,
whales and dolphins, said corresponding author Albert S. Feng, a
professor of
molecular
and integrative physiology at the University of Illinois at
Urbana-Champaign. Feng, a researcher at the
Beckman Institute for
Advanced Science and Technology, was introduced to the frog
species by Kraig Adler, a Cornell University biologist who had
learned about it while conducting a survey of amphibians in China.
Feng continues to study frogs and bats to understand how the brain
processes sound patterns, especially in sound-cluttered environments
in which filtering is required to allow for communication.
Feng and colleagues previously reported that males of the species
make these high-pitched birdlike calls, with numerous variants in
terms of harmonics and frequency sweeps. Some sounds exceeded their
recording device's maximum capability of 128 kilohertz. Human ears
hear sound waves generally no higher than 20 kilohertz. The frogs
studied inhabit Huangshan Hot Springs, a popular, scenic mountainous
area west of Shanghai that is alive with noisy waterfalls and
wildlife.
"Nature has a way of evolving mechanisms to facilitate
communication in very adverse situations," Feng said. "One of the
ways 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. Frogs
were never taken into consideration for being able to do this."
Adler had drawn attention to the species because the frogs do not
have external eardrums, raising the possibility of unusual hearing
abilities. "Now we are getting a better understanding of why their
eardrums are recessed," Feng said. "Thin eardrums are needed for
detection of ultrasound. Recessed ears shorten the path between
eardrums and the ear, enabling the transmission of ultrasound to the
ears."
To test if the frogs actually communicated with their ultrasonic
sounds, Feng and colleagues returned to China with their recording
equipment and a special device that allowed playback of recorded
frog calls in the audible or ultrasonic ranges. The researchers
observed eight male frogs under three experimental conditions: no
sounds, playback of calls containing only audible parts and playback
of just ultrasonic frog calls.
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 During playback, the researchers watched for evoked calling
activity, in which a male frog begins calling upon hearing calls
from other frogs in the area. Five frogs responded to ultrasonic and
audible sound ranges, with four responding with calls in both
ranges. One frog called 18 times to ultrasonic calls, including four
very telling rapid responses, Feng said. Another frog did not
respond to ultrasonic stimulation but produced calls 18 times to an
audible prompt.
Clearly, Feng said, some of the frogs indeed communicated
ultrasonically. They have the ability to do so, but for some reason
some frogs do and some don't, he said. "We believe that all of them
have the capacity to respond to the ultrasound."
Ultrasonic communication likely will be found in other amphibians
and birds, Feng said, but, until now, no one has bothered to look
into it.
"Humans have always been fascinated by how some animals can
discern their world through a sensing system vastly different from
our own," Feng said. "The electromagnetic sense in fishes and homing
pigeons, polarized light vision in ants, chemical sensing of
pheromones in insects and rodents, echolocation by ultrasound in
bats and dolphins are just a few examples.
"That frogs can communicate with ultrasound adds to that list and
represents a novel finding because we normally think such ability is
limited to animals equipped with a sophisticated sonar system," he
said. "This suggests that there are likely many other examples of
unexpected forms of communication out there."
The eight authors were Feng; Wen-Yu Lin, a senior research
scientist in Feng's lab; Peter M. Narins of the University of
California at Los Angeles; Chun-He Xu of the Shanghai Institutes of
Biological Sciences, Chinese Academy of Sciences, in Shanghai; and
Zu-Lin Yu, Qiang Qiu, Zhi-Min Xu and Jun-Xian Shen of the State Key
Laboratory of Brain and Cognitive Science, Institute of Biophysics,
Chinese Academy of Sciences, in Beijing.
Feng and Narins received funding from the National Institute on
Deafness and Other Communication Disorders, one of the National
Institutes of Health. Feng also was funded by the National Science
Foundation. Additional Chinese grants from the State Key Basic
Research and Development Plan and the National Natural Sciences
Foundation to Chun-He Xu and Shen, respectively, supported the work.
[Jim Barlow, life sciences editor,
University
of Illinois at Urbana-Champaign news bureau] |
