Physiological Mechanisms Mediating Ultrasonic Detection and Production in Amphibians

University Of California-Los Angeles, Los Angeles CA

Investigators

Abstract

This novel finding that some Asian frogs can communicate and are sensitive to ultrasound motivates the proposed studies to examine the similarities and differences in the high-frequency/ultrasonic communication systems of the Chinese and Bornean frogs to obtain new insights into the mechanisms underlying vertebrate high-frequency communication. With the discovery of three species of frogs that communicate with ultrasonic frequencies, the field is wide open for the exploration of the mechanisms underlying ultra-high frequency transduction in a tractable vertebrate model system. Modern electrophysiological techniques will be used to examine the middle ear (tympanic membrane) and inner ear characteristics of two of the three known ultrasonically communicating frogs, and laser Doppler vibrometry will pinpoint the mechanisms for ultrasound production in these animals. This work will likely provide important new insights into the electrical and mechanical processes that underlie high-frequency tuning properties of the vertebrate auditory periphery. The unexpected ultrasonic sensitivity in anuran amphibians illustrates the remarkable adaptability of the auditory system and the extent to which evolution can modify a sensory system to adapt to its environment. Moreover, interest in these species in China and Borneo has already begun to promote long-term conservation of the habitats of these extraordinary animals. The results of this project will provide essential information on amphibian auditory physiology which will be of broad interest to conservation biologists project and would be incorporated into public outreach lectures through the Los Angeles County Museum. The proposed experiments will test four clear hypotheses: 1: The middle and inner ears of the ultrasonic frogs exhibit adaptations for the detection of high frequencies. DPOAE measurements and laser Doppler vibrometry will be utilized to characterize in detail the auditory periphery of Odorrana- a Chinese frog which has been shown to produce and detect ultrasounds. 2: A quantitative test of the hypothesis that the DPOAE is present in the high-frequency mechanical input to the hair cell bundle in the amphibian papilla and the basilar papilla of the inner ear will be performed. A mechanical stimulus consisting of two tones of equal level will be introduced and the characteristics of resulting hair bundle motions will be investigated using a high-speed probe stimulation and imaging system. 3: The source of the ultrasonic sensitivity is the basilar papilla of the inner ear. This will be examined in two species of Asian frogs known to both produce and detect ultrasound, O. graminea and H. cavitympanum. Intracellular recordings made from ultra-high-frequency eighth nerve fibers in these frogs, followed by dye-filling and fiber tract tracing will enable the unambiguous mapping of the distal portions of these fibers to their origins in the inner ear. 4: Ultrasonic vocalization components of the frog's advertisement call are produced by the cranial portion of the medial vocal ligament (mlcr) in the larynx. The specific mechanisms used by the larynges of the frogs, O. graminea and H. cavitympanum, to produce high-frequency call elements will be investigated. The activated larynx preparation will be utilized which consists of forcing air through the larynx of euthanized males and measuring the resulting motion of at several points along the vocal folds, in addition to the mlcr, using a single-point laser Doppler vibrometer.