A High-Frequency Siren Song
http://sciencenow.sciencemag.org/cgi/content/full/2008/512/5?etoc
By Lauren Cahoon
/Science/NOW Daily News
12 May 2008
Female frogs aren't known as great communicators. Although they may
squeak when caught by a predator, they spend most of their lives in
silence. A new discovery could change this notion: Researchers have
found that the female concave-eared torrent frog makes a high-pitched
peep to attract nearby males. The call is a genuine siren song: Upon
hearing it, males leap toward the source with uncanny accuracy, even in
darkness, rivaling the localization abilities of owls, dolphins, and
humans.
Male concave-eared torrent frogs (/Odorrana tormota/) communicate their
whereabouts and their availability as mates by means of ultrasonic
calls. The high frequency of the sound allows the frogs to be heard over
the noisy rapids of their home environment, the Huangshan hot springs in
China. Biophysicists led by Jun-Xian Shen of the Chinese Academy of
Sciences in Beijing suspected that female frogs were capable of making
similar calls when they dissected the females and found that, like the
males, they had large larynxes--a trait that separated them from females
of other frog species.
The team then caught a number of females and brought them into the
laboratory to determine if they could sing like males. Sure enough, the
female concave-eared torrent frog had the rare ability to call out like
males--however, instead of constantly calling like males do, the females
only called just before laying their eggs; after that, they stayed silent.
To see if this siren song helped male frogs find a female, the
researchers brought 41 male frogs into a darkened laboratory and played
a female's call on a loudspeaker. The males responded by calling back
and leaping--sometimes in a single hop--directly to the speaker,
evincing as much accuracy at homing in on a noise as is typical for
expert species such as humans and dolphins. "The precision with which
the males found the loudspeaker is shocking," says co-author Albert
Feng, a neuroscientist at the University of Illinois, Urbana-Champaign.
"We, frankly, didn't think that the frogs had this kind of ability."
Feng notes that the homing talent is unusual in such small creatures.
Normally, animals need to have larger heads with more widely spaced ears
in order to locate sounds with accuracy, he says. One possibility is
that the frequency of a female's call is so high that the waves bounce
off of the listener's head, amplifying the difference in sound level
between one ear and the other. This makes the sound that much more
intense and easy to detect, the team reports online this week in
/Nature/. Low-frequency waves travel around the listener without this
effect.
Darcy Kelley, a biologist at Columbia University, is surprised by the
reversal of gender roles. "Females that have a fertility advertisement
call--that's pretty unusual," she says.
Senior author Peter Narins, a biologist at the University of California,
Los Angeles, believes that the results will increase our understanding
of the hearing mechanisms in both frogs and humans. Because frogs are
champions at picking out their preferred mate's voice from a chorus of
competitors, these animals may help scientists create a more
sophisticated hearing aid, for example. "The frog is really a fabulous
model of hearing," says Narins. "The more we can learn about hearing and
localization in frogs, the more we can learn about human hearing."
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