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Hearing with an atympanic ear: good vibration and poor sound-pressure detection in the royal python, Python regius

Lookup NU author(s): Dr Christian Brandt

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Abstract

Snakes lack both an outer ear and a tympanic middle ear, which in most tetrapods provide impedance matching between the air and inner ear fluids and hence improve pressure hearing in air. Snakes would therefore be expected to have very poor pressure hearing and generally be insensitive to airborne sound, whereas the connection of the middle ear bone to the jaw bones in snakes should confer acute sensitivity to substrate vibrations. Some studies have nevertheless claimed that snakes are quite sensitive to both vibration and sound pressure. Here we test the two hypotheses that: (1) snakes are sensitive to sound pressure and (2) snakes are sensitive to vibrations, but cannot hear the sound pressure per se. Vibration and sound-pressure sensitivities were quantified by measuring brainstem evoked potentials in 11 royal pythons, Python regius. Vibrograms and audiograms showed greatest sensitivity at low frequencies of 80–160Hz, with sensitivities of –54 dB re.1ms–2 and 78 dB re. 20 ymPa, respectively. To investigate whether pythons detect sound pressure or sound-induced head vibrations, we measured the sound-induced head vibrations in three dimensions when snakes were exposed to sound pressure at threshold levels. In general, head vibrations induced by threshold-level sound pressure were equal to or greater than those induced by threshold-level vibrations, and therefore sound-pressure sensitivity can be explained by sound-induced head vibration. From this we conclude that pythons, and possibly all snakes, lost effective pressure hearing with the complete reduction of a functional outer and middle ear, but have an acute vibration sensitivity that may be used for communication and detection of predators and prey.

Publication metadata

Author(s): Christensen CB, Christensen-Dalsgaard J, Brandt C, Madsen PT

Publication type: Article

Publication status: Published

Journal: Journal of Experimental Biology

Year: 2011

Volume: 215

Issue: 2

Pages: 331-342

Print publication date: 27/10/2011

ISSN (print): 0022-0949

ISSN (electronic): 1477-9145

Publisher: The Company of Biologists Ltd.

URL: http://dx.doi.org/10.1242/jeb.062539

DOI: 10.1242/jeb.062539

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