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  • The Royal Society  (2)
  • 1
    In: Biology Letters, The Royal Society, Vol. 7, No. 1 ( 2011-02-23), p. 139-141
    Abstract: Lungfishes are the closest living relatives of the tetrapods, and the ear of recent lungfishes resembles the tetrapod ear more than the ear of ray-finned fishes and is therefore of interest for understanding the evolution of hearing in the early tetrapods. The water-to-land transition resulted in major changes in the tetrapod ear associated with the detection of air-borne sound pressure, as evidenced by the late and independent origins of tympanic ears in all of the major tetrapod groups. To investigate lungfish pressure and vibration detection, we measured the sensitivity and frequency responses of five West African lungfish ( Protopterus annectens ) using brainstem potentials evoked by calibrated sound and vibration stimuli in air and water. We find that the lungfish ear has good low-frequency vibration sensitivity, like recent amphibians, but poor sensitivity to air-borne sound. The skull shows measurable vibrations above 100 Hz when stimulated by air-borne sound, but the ear is apparently insensitive at these frequencies, suggesting that the lungfish ear is neither adapted nor pre-adapted for aerial hearing. Thus, if the lungfish ear is a model of the ear of early tetrapods, their auditory sensitivity was limited to very low frequencies on land, mostly mediated by substrate-borne vibrations.
    Type of Medium: Online Resource
    ISSN: 1744-9561 , 1744-957X
    Language: English
    Publisher: The Royal Society
    Publication Date: 2011
    detail.hit.zdb_id: 2103283-X
    SSG: 12
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  • 2
    Online Resource
    Online Resource
    The Royal Society ; 2012
    In:  Proceedings of the Royal Society B: Biological Sciences Vol. 279, No. 1736 ( 2012-06-07), p. 2237-2245
    In: Proceedings of the Royal Society B: Biological Sciences, The Royal Society, Vol. 279, No. 1736 ( 2012-06-07), p. 2237-2245
    Abstract: Animals that use echolocation (biosonar) listen to acoustic signals with a large range of intensities, because echo levels vary with the fourth power of the animal's distance to the target. In man-made sonar, engineers apply automatic gain control to stabilize the echo energy levels, thereby rendering them independent of distance to the target. Both toothed whales and bats vary the level of their echolocation clicks to compensate for the distance-related energy loss. By monitoring the auditory brainstem response (ABR) during a psychophysical task, we found that a harbour porpoise ( Phocoena phocoena ), in addition to adjusting the sound level of the outgoing signals up to 5.4 dB, also reduces its ABR threshold by 6 dB when the target distance doubles. This self-induced threshold shift increases the dynamic range of the biosonar system and compensates for half of the variation of energy that is caused by changes in the distance to the target. In combination with an increased source level as a function of target range, this helps the porpoise to maintain a stable echo-evoked ABR amplitude irrespective of target range, and is therefore probably an important tool enabling porpoises to efficiently analyse and classify received echoes.
    Type of Medium: Online Resource
    ISSN: 0962-8452 , 1471-2954
    Language: English
    Publisher: The Royal Society
    Publication Date: 2012
    detail.hit.zdb_id: 1460975-7
    SSG: 12
    SSG: 25
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