Concave-eared Torrent Frog
Males have ear canals with recessed tympanic membranes at the end of the canals, like mammals but unlike all other anurans except for Huia cavitympanum (Feng et al. 2002). In Odorrana tormota, the tympanic membranes have been shown to be exceptionally thin, which facilitates transmission of high-frequency sounds to the inner ear (Feng et al. 2006). The middle ear bones (ossicles) are reduced in both size and mass, due to the shortened distance between the tympanum and inner ear; this also facilitates high-frequency sound transmission (Feng et al. 2006).
Males also have two pairs of vocal sacs (Feng et al. 2002). In addition, the larynx appears to be specialized for production of ultrasound frequencies and the generation of calls with nonlinear features such as subharmonics and chaos (Suthers et al. 2006). These specializations include variations in thickness along the lengths of the vocal cords, and reverse size dimorphism, with males having smaller larynxes (about half as large as that of the female), unlike other anuran species (Suthers et al. 2006).
Distribution and Habitat
Life History, Abundance, Activity, and Special Behaviors
This frog is one of only two anuran species (the other being Huia cavitympanum) that has been shown to communicate using ultrasound (frequencies above 20 kHz), which is extremely unusual in non-mammalian vertebrates (Feng et al. 2002; Feng et al. 2006; Arch et al. 2008). Male Odorrana tormota make melodic calls resembling those of birds, with distinct frequency modulations that are primarily in the audible range (5-9 kHz) but often reach into the ultrasonic range (Feng et al. 2002; Feng et al. 2006; Arch et al. 2008).
Males are territorial and call from low vegetation adjacent to noisy streams, with calling males spacing themselves at about 1.5 m apart (Feng et al. 2002). The calls consist of either two notes of short tone "pips" or a single note with short or long duration, all of which have very variable components (Narins et al. 2004). However, unlike other anurans, which have a limited repertoire of calls typical of each species, Odorrana tormota has a vocal repertoire that cannot be accurately estimated in size; analysis of 12 hours of tape from 21 calling males revealed no two calls alike (Feng et al. 2002). (In contrast, the frog Boophis madagascariensis from Madagascar makes 28 distinct calls, by far the most previously described for any anuran species (Narins et al. 2000).)
The unusually rich and complex vocal repertoire of Odorrana tormota shares aspects of passerine bird, primate, or whale sounds, such as ultrasonic components, musical warbling (multiple upward and downward frequency modulation sweeps), and sudden onset/cessation of selective harmonic components within a single call note (Feng et al. 2002). Males have two pairs of vocal sacs, which contributes to the harmonic complexity of the call (Feng et al. 2002), as well as a specialized larynx (Suthers et al. 2006). Laryngeal specializations include unusually intricate vocal cord morphology, with varying thickness along their length; very thin portions of the medial vocal ligaments appear to contribute to ultrasound production (Suthers et al. 2006). Both the ultrasound frequencies and the nonlinear dynamics (subharmonics and chaos) associated with the calls of this species may thus arise from complex nonlinear oscillatory patterns of the vocal cords (Suthers et al. 2006). In addition, there is reverse sexual size dimorphism of the larynx; unlike all other frogs examined to date, which have larger larynxes in the male than the female, in O. tormotus the male larynx is smaller than that of the female (Suthers et al. 2006). Interestingly, most of the acoustic features present in normal male Odorrana tormota vocalizations can be generated by forcing airflow through the larynx of a euthanized frog (Suthers et al. 2006).
Electrophysiological recordings from the auditory midbrain confirm that this species can hear as well as generate ultrasound (Feng and Narins 2007). Hearing in this species spans the range from less than 1 kHz to about 35 kHz (Narins et al. 2004; Feng et al. 2006), which is a considerably higher range than had previously been thought to exist for anurans (up to 5-8 kHz, Fay 1988; Loftus-Hills and Johnstone 1970). It is not known what organ within the ear is responsible for ultrasonic sensitivity (Feng et al. 2006). Frogs have two known auditory organs, the amphibian papilla, which responds to low/intermediate frequencies, and the basilar papilla, which responds to high frequencies (Feng et al. 1975; Lewis and Narins 1999). The upper limit for frog hearing was previously thought to be 8.2 kHz, based on the sensitivity recorded for basilar papilla nerve fibers (Loftus-Hills and Johnstone 1970). Thus either the upper frequency sensitivity has been dramatically increased for the basilar papilla in this species, or another as yet undescribed mechanism is responsible for the detection of ultrasonic calls (Arch et al. 2008).
In addition to being heard, the ultrasound components of the call do function in male-male interaction, since playback of both ultrasonic and audible components of recorded calls evoked vocal responses from males (Feng and Narins 2007).
While ultrasound is used and perceived in male-male territorial interactions in this species, it is not clear whether ultrasound is also involved in male-female communication. Males have recessed tympanic membranes, whereas females do not (Chen 1991).
This species shelters in moist rock crevices during the day, and is found in thick brush alongside streams at night (Fei 1999).
The reproductive season begins in June. Eggs are milky yellow in color, and measure about 2 mm in diameter (Fei 1999).
Possible reasons for amphibian decline
Habitat modification from deforestation, or logging related activities
This species (Odorrana tormota) was formerly known as Amolops tormotus.
The two frog species with ultrasound communication (Odorrana tormota and Huia cavitympanum) are both found in Southeast Asia but are neither sympatric nor closely related (Cai et al. 2007; Stuart 2007). Rather, they are found in similar habitats, with males calling adjacent to noisy, rushing streams (Arch et al. 2008).
A related species from the same province, Odorrana livida, also has the ability to detect ultrasound, as shown by recordings from the auditory midbrain. Odorrana livida has very thin, transparent tympanic membranes, but in this species the membranes are not recessed. It has not yet been shown whether Odorrana livida is also emitting ultrasonic frequencies in its calls (Feng et al. 2006).
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Suthers, R. A., Narins, P. M., Lin, W.-Y., Schnitzler, H.-U., Denzinger, A., Xu, C.-H., and Feng, A. S. (2006). ''Voices of the dead: complex nonlinear vocal signals from the larynx of an ultrasonic frog.'' Journal of Experimental Biology, 209, 4984-4993.
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Written by Kellie Whittaker and David Chen (biologist AT earthlink.net), UC Berkeley
First submitted 2000-08-08
Edited by Kellie Whittaker (2008-08-11)
Species Account Citation: AmphibiaWeb 2008 Odorrana tormota: Concave-eared Torrent Frog <http://amphibiaweb.org/species/4661> University of California, Berkeley, CA, USA. Accessed Dec 2, 2016.
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Citation: AmphibiaWeb. 2016. <http://amphibiaweb.org> University of California, Berkeley, CA, USA. Accessed 2 Dec 2016.
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