Frog Ears and Ultrasonic Playback

The first amphibian known to call exclusively in the ultrasonic is identified!

"You look at the frog and can see it is vocalizing — you can tell because their vocal pouches pulsate — but you don't hear any sound. It's amazing. Then you look down at the recording equipment and see the lights flashing, indicating sound. I have never seen that before. In a frog, it's unprecedented to have purely ultrasonic vocalizations." Victoria Arch, UCLA grad student.

The “hole-in-the- head” frog (Huia cavitympanum) - so called because of its recessed ear drums- resides in hillside forest ecosystems of Borneo and Southeast Asia at elevations between 250 and 1000 meters. It is unique among the Ranidae for its ability to vocalize and hear ultrasound calls – well outside of the human range of hearing.

According to Victoria Arch, one of the authors of a recent paper published at PLoS One describing the communication of Huia cavitympanum, "Our hypothesis is that these frogs have shifted to use higher frequencies in their communication to avoid the interference of sound produced by rushing water in the lower-frequency range. However, high-frequency sounds do not transmit as far. By producing some lower-frequency calls, they can transmit calls over a greater distance, so they can communicate with frogs that are farther away. But by also producing some calls that are high-frequency — all ultrasonic — they may be able to communicate better over that background noise. Producing both types of calls might be a bet-hedging strategy to be heard," Arch said. "This is how males attract females, communicate with one another and establish territorial boundaries."

H. cavitympanum relies on fast moving streams for reproduction; these sometimes torrential waters may have necessitated enhanced communication tactics in order to affectively stake out territories and attract potential mates. The tadpoles of the species have also adapted to streamside existence - they’ve developed huge abdominal suckers in order to suction-cup themselves to the sides of rocks.

Abstract (Full Article Here)

Huia cavitympanum, an endemic Bornean frog, is the first amphibian species known to emit exclusively ultrasonic (i.e., >20 kHz) vocal signals. To test the hypothesis that these frogs use purely ultrasonic vocalizations for intraspecific communication, we performed playback experiments with male frogs in their natural calling sites. We found that the frogs respond with increased calling to broadcasts of conspecific calls containing only ultrasound. The field study was complemented by electrophysiological recordings from the auditory midbrain and by laser Doppler vibrometer measurements of the tympanic membrane's response to acoustic stimulation. These measurements revealed that the frog's auditory system is broadly tuned over high frequencies, with peak sensitivity occurring within the ultrasonic frequency range. Our results demonstrate that H. cavitympanum is the first non-mammalian vertebrate described to communicate with purely ultrasonic acoustic signals. These data suggest that further examination of the similarities and differences in the high-frequency/ultrasonic communication systems of H. cavitympanum and Odorrana tormota, an unrelated frog species that produces and detects ultrasound but does not emit exclusively ultrasonic calls, will afford new insights into the mechanisms underlying vertebrate high-frequency communication.

Photographic Credits: Frogs of Borneo

Arch, V., Grafe, T., Gridi-Papp, M., & Narins, P. (2009). Pure Ultrasonic Communication in an Endemic Bornean Frog PLoS ONE, 4 (4) DOI: 10.1371/journal.pone.0005413

University of California, Los Angeles (2009, May 9). Ultrasonic Communication Among Frogs. ScienceDaily. Retrieved May 9, 2009, from http://www.sciencedaily.com/releases/2009/05/090508192231.htm
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