A frog’s lungs sharpen the frequency tuning of its peripheral auditory system: A pulmonary paradox resolved?

Abstract

In frogs, sound localization is facilitated by the directionality of their internally coupled ears, which are connected through the mouth cavity and Eustachian tubes. Acoustic input through the frog’s body wall and lungs also shapes the ear’s directionality. One hypothesized function of the lung input is to enhance directional hearing to improve localization of conspecific calls. However, an unresolved paradox exists: the lung input often improves directionality at frequencies that are intermediate between those emphasized in conspecific vocalizations. The present study of green treefrogs (Hyla cinerea) may resolve this paradox. Using laser vibrometry, we show that the lung input improves directionality at frequencies emphasized in conspecific calls by just 2 dB or less. In contrast, the lung input reduces the frontal field sensitivity of the tympanum by up to 7 dB in response to frequencies that are intermediate between those emphasized in conspecific calls and to which the two inner ear papillae are tuned. These results suggest the lung input may function in communication by sharpening the frequency tuning of the peripheral auditory system, which in turn could filter out frequencies in heterospecific calls in some mixed-species choruses. How the lung input achieves this “noise cancellation” is currently under investigation.