Amphibian underwater hearing: Biophysics and neurophysiology

Christensen-Dalsgaard, J. (Foredragsholder)

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 Many frog species produce underwater mating calls and are presumably specialized for underwater hearing. Some are terrestrial outside the mating season and without evident specializations for underwater hearing when compared to their closest relatives. However, ears of obligate aquatic frogs such as Xenopus show modifications most likely caused by such specialization.

Like terrestrial frogs,  Xenopus laevis has a tympanic ear, but the eardrum is a cartilaginous disk covered by skin and fat. The middle ear is air-filled when the frog is submerged, and it has been shown that the eardrum movements are largely caused by resonance of the enclosed air in the middle ear cavities and the lungs (Christensen-Dalsgaard and Elepfandt, JCP A 176:317-24, 1995), resulting in maximal sensitivity around 1.6 kHz (the dominant frequency of the advertisement call).

The eardrum movements are coupled to the inner ear by the columella. Responses of neurons in the auditory pathway shows that the call temporal pattern is accurately represented in the auditory nerve and first auditory nucleus, but that this temporal representation is degraded in the midbrain, where instead rate-selective cells occur. The lowest thresholds of the auditory nerve fibers are-77 dB re 1 pa at the advertisement call frequencies, corresponding to a detection distance of 30-40 m in the shallow water ponds that Xenopus inhabits.

Periode14. aug. 2007
BegivenhedstitelInternational conference on the effects of noise on aquatic life: null