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Researchers Explore the Relationship between Morphological Structures and Functions of Ultrasonic Frogs

Update time: 12/05/2012 Author: XIONG Rongchuan & JIANG Jianping

Concave-eared frog (Odorrana tormota), a famous endemic amphibian animal in eastern China, is named after its recessed tympanic membranes, like mammals but unlike all other anurans except for Huia cavitympanum which is endemic in Borneo. The unique morphological structure inspired the enthusiasm of biologists to study its sound communication model. And then it was found to communicate with ultrasound (frequencies above 20 kHz), which is extremely unusual in non-mammalian vertebrates.　

Prof. JIANG Jianping’s group from Chengdu Institute of Biology, Chinese Academy of Sciences has long been committed to the study of amphibians, especially the endemic anuran species that distribute in China. Recently, Dr. XIONG Rongchuan conducted by Prof. JIANG Jianping, found that O. tormota possesses specialized phonating organ structures, which might be favored by higher frequency of phonation of O. tormota.

This group have surveyed the life history of the Concave-eared frogin the field, Huangshan in Anhui province, for several years. During the observations, they found that the male frogs usually showed strong respiratory movements when they called. Usually call generation of most frogs is closely tied to their buccopharyngeal respirations.

Firstly air is sucked in through the nostrils to fill the buccopharyngeal cavity, and then the expanded mouth floor contracts. This forces the air from the buccopharyngeal cavity into the lungs. To call, they take up a large volume of air into the mouth cavity and lungs via several buccal oscillation and lung inflation cycles, and then the air is expelled out to vibrate the vocal cords for sound producing. So they presumed that the ultrasonic frog may has a more powerful mouth floor to support the faster airflow during the sound producing to drive the vocal cords (sound source of frogs) vibrating at higher frequencies, compared to other non-ultrasonic frogs. .

The research team employed anatomic and histological methods to examine the vocal organs, including the floor of the buccal cavity, vocal cords and glottis, of Odorrana tormota and its sympatric species including O. graminea, O. schmackeri, and Amolops wuyiensis with different fundamental frequencies, and Pelophylax nigromaculatus as a control.

Their result showed that the Concave-eared frog has thinner vocal cords modulated by a moderately stronger muscular mastoideus between the medial vocal cords and the lateral cricoid cartilages, larger relative distance between the two m. intermandibulares (RDMI), and higher nucleus density of m. intermandibularis (NDMI) and m. geniohyoideus (NDMG). All these characters make the buccopharyngeal cavity of the concave-eared frog a powerful air pump to supply fast airflow which drives the thin vocal cords vibrating to produce high-frequencies phonating.

This work provides guidance for future biophysics studying about the phonatingmechanism of ultrasonic frog. It is also in favor of future electrophysiological experiments and tracing experiments molecular network to supply a reference in choosing aim organs.　The paper entitled "Morphological Correlates of the Phonatory Organ in an Ultrasonically Phonating Frog" was published on the Asian Herpetological Research. (2012, 3 (3), 240-251).