Meeting Abstract

S1.2  Sunday, Jan. 4  High frequency hearing and behavioral tuning of the ear in frogs GRIDI-PAPP, M.*; FENG, A.S.; SHEN, J.-X.; YU, Z.-L.; ROSOWSKI, J.J.; NARINS, P.M.; Univ. of California, Los Angeles; University of Illinois, Urbana; Chinese Academy of Sciences, Beijing; Chinese Academy of Sciences, Beijing; Harvard Medical School, Boston; Univ. of California, Los Angeles mgpapp@ucla.edu

The upper frequency limit of anuran communication has been recently raised from 5-8 kHz to 34 kHz by studies on the Chinese concave-eared torrent frog (Odorrana tormota, Ranidae). Here we report on the mechanics of high frequency hearing and ear tuning in this species. The eardrums exhibit a broad response to acoustic stimulation with peak vibration velocity at 7 kHz, and high frequencies are transmitted across the stapes. Odorrana tormota can actively close its Eustachian tubes (ETs), falsifying the common belief that ETs in amphibians stay permanently open. The frogs close their ETs by contracting the submaxillary and petrohyoid muscles, which cause pivoting of the anterior hyoid horn over its attachment to the skull. Eustachian tube closure shifts the acoustic sensitivity of the middle ear, producing up to 20 dB gain above 10 kHz and up to 26 dB attenuation below 10 kHz. Such shift is the effect of reducing the volume of the air cavity behind the eardrum. When the ET closes, the connection between the middle ear and the large buccal volume is lost and the compliance of the middle ear cavity is reduced, stiffening the eardrum. Behavioral monitoring in the field has confirmed ET closure during the phonatory phase of each call and during swallowing. Several non-exclusive potential roles for ET closure are being examined, including: protection of the inner ear from intense sound or high air pressure during calling; reduction of acoustic masking of conspecific calls by stream noise or self-generated vocalizations; and protection of the thin eardrums from injury by life prey in the mouth.