humans, and far higher than the 12 kHz frequencies that most amphibians, reptiles, and birds are capable of hearing and producing. Key parts of the ear must be specially adapted to detect ultrasounds namely, the eardrum must be very thin to vibrate effectively at these high frequencies, and the bones of the middle ear must be extremely lightweight in order to transmit ultrasonic vibrations to the inner ear. The presence of an ear canal not only protects A. tormotus's thin and fragile eardrum from the environment but also lessens the distance between the eardrum and the inner ear, thus allowing the bones of the middle ear to be shorter, and as a result, lighter in weight.

Researchers have known for several years that A. tormotus males produce high-pitched, birdlike calls that extend into the ultrasonic range. What remained to be tested was whether the ultrasounds were a byproduct of the frog's sound production system or were heard and responded to by other males of that species. Researchers Albert S. Feng, Ph.D., an auditory neuroscientist at the University of Illinois, Urbana-Champaign, and Peter M. Narins, Ph.D., who studies auditory behavior, neurophysiology, and mechanics at the University of California, Los Angeles, and collaborators conducted behavioral and physiological studies to investigate A. tormotus's hearing ability.

The researchers first wanted to know if A. tormotus can hear ultrasounds. They recorded a male's call, split it into the audible components and ultrasonic components, and observed the responses of eight A. tormotus males to each of the split sounds. Five of the eight frogs produced calls in response to the audible, ultrasonic, or both components of the species call and three did not. Results of the behavioral observations showed that males were capable of hearing and responding to ultrasounds.

The researchers then measured the electrical activities in A. tormotus's midbrain that is involved in
'"/>

Contact: Jennifer Wenger
jwenger@mail.nih.gov
301-496-7243
NIH/National Institute on Deafness and Other Communication Disorders
15-Mar-2006

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