Snakes hear by detection of sound-induced skull vibrations
-
1
Aarhus University, Zoophysiology, Bioscience, Denmark
-
2
University of Southern Denmark, Biology, Denmark
All terrestrial vertebrates face the problem of impedance mismatch between air and tissue and hence the problem of getting sound energy into the inner ear to stimulate hair cells. The most common solution to this problem is the tympanic middle ear that transforms the sound energy in air to fluid motion in the inner ear. Having evolved independently in all the major tetrapod linages, the tympanic middle ear has played a crucial role in evolutionary transition from water to air. Some tetrapods have, nonetheless, secondarily lost their tympanum and middle ear. One is example is the snakes that all have a reduced tympanic cavity and no tympanum or Eustachian tubes. Snakes have, however, maintained the middle ear ossicle, which instead of being connected to a tympanum, is connected to quadrate of the jaw apparatus. This secondary reduction compared to other tetrapod groups is presumably attributable to the evolution of the ophidian feeding mechanism where the jaws are used to manipulate prey. Snakes would therefore be hypothesized to have very poor pressure hearing and generally be insensitive to airborne sound, whereas the connection of 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. In this study 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. To do that, vibration and sound pressure sensitivities were quantified by measuring brainstem evoked potentials in 11 royal pythons (Python regius). Vibrograms and audiograms show best sensitivity at low frequencies of 80-160 Hz with sensitivities of -54 dB re 1 m/s2 and 78 dB re 20 Pa, respectively. To investigate whether pythons detect sound pressure per se, or detect sound-induced vibrations of substrate or head, we measured these vibrations in three dimensions when exposed to sound pressure at threshold levels. Sound-induced substrate vibrations only exceed vibration thresholds at the lowest frequencies, and therefore cannot explain the sound pressure sensitivity. However, head vibrations induced directly by threshold-level sound pressure are, equal to or greater than head vibrations 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 that they have an acute vibration sensitivity that may be used for communication and detection of predators and prey.
Keywords:
Hearing,
Python regius,
Snake,
Vibration detection
Conference:
Tenth International Congress of Neuroethology, College Park. Maryland USA, United States, 5 Aug - 10 Aug, 2012.
Presentation Type:
Poster (but consider for student poster award)
Topic:
Sensory: Audition
Citation:
Bech Christensen
C,
Christensen-Dalsgaard
J,
Brandt
C and
Madsen
P
(2012). Snakes hear by detection of sound-induced skull vibrations.
Conference Abstract:
Tenth International Congress of Neuroethology.
doi: 10.3389/conf.fnbeh.2012.27.00110
Copyright:
The abstracts in this collection have not been subject to any Frontiers peer review or checks, and are not endorsed by Frontiers.
They are made available through the Frontiers publishing platform as a service to conference organizers and presenters.
The copyright in the individual abstracts is owned by the author of each abstract or his/her employer unless otherwise stated.
Each abstract, as well as the collection of abstracts, are published under a Creative Commons CC-BY 4.0 (attribution) licence (https://creativecommons.org/licenses/by/4.0/) and may thus be reproduced, translated, adapted and be the subject of derivative works provided the authors and Frontiers are attributed.
For Frontiers’ terms and conditions please see https://www.frontiersin.org/legal/terms-and-conditions.
Received:
25 Apr 2012;
Published Online:
07 Jul 2012.
*
Correspondence:
Mr. Christian Bech Christensen, Aarhus University, Zoophysiology, Bioscience, Aarhus, Denmark, christian.bech@biology.au.dk