Title

Amphibian communication: coupling of eardrums to the medium at the air-water interface

Poster Number

32

Lead Author Affiliation

Biology

Introduction

Reproduction in many animals depends on females detecting and responding to male advertisement calls. Effective communication requires the frequency sensitivities of the ear and brain to be tuned to the call’s frequency. In anurans, female ears and male calls are normally found to be tuned to the same frequencies. However, in túngara frogs (Engystomops pustulosus), we have observed a discrepancy: the eardrum is most sensitive to frequencies around 2.2 kHz, which is much higher than the frequencies to which the male calls are tuned (600 Hz). Curiously, the sensitivity of the auditory regions of the brain matches the tuning of the calls, but not that of the eardrums.

Purpose

To determine if underwater hearing by the female in the final approach of the male explains the mismatch between the tuning of the eardrum and that of the brain in air.

Method

Female frogs were put into clear, plastic tanks and photographed. Anesthetized frogs and simplistic artificial models (made of cryogenic tubes with latex membranes), which had reflective patches glued onto the eardrum and membrane respectively, were placed 1 cm underwater into a water-filled glass terrarium. A scale of frequencies was played through a shaker (placed against the wall of the terrarium) or speaker (positioned at a corner of the terrarium) and membrane vibrations were detected using a Doppler laser.

Results

Ovulating females float with their ears fully submerged and their eyes and nares partially submersed, whereas post-ovulation females have ears fully submerged and eyes and nares completely out of the water. Doppler laser vibrometry experiments revealed that the eardrums shifted its tuning to around half the frequency to which it was tuned in air. This result was not verified in the artificial model, in which the change in medium produced some change in the relative amplitudes of vibration peaks, but it did not shift the response spectrum in general, as it did with the natural ears.

Significance

This study revealed a system that is uniquely suited for testing hypotheses involving the effect of transmission medium in the design and performance of acoustic signals calling apparatuses and ears.

Location

DeRosa University Center, Stockton campus, University of the Pacific

Format

Poster Presentation

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Amphibian communication: coupling of eardrums to the medium at the air-water interface

DeRosa University Center, Stockton campus, University of the Pacific

Reproduction in many animals depends on females detecting and responding to male advertisement calls. Effective communication requires the frequency sensitivities of the ear and brain to be tuned to the call’s frequency. In anurans, female ears and male calls are normally found to be tuned to the same frequencies. However, in túngara frogs (Engystomops pustulosus), we have observed a discrepancy: the eardrum is most sensitive to frequencies around 2.2 kHz, which is much higher than the frequencies to which the male calls are tuned (600 Hz). Curiously, the sensitivity of the auditory regions of the brain matches the tuning of the calls, but not that of the eardrums.