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Temporal resolution of the Florida manatee (Trichechus manatus latirostris) auditory system

David A Mann1, Debborah E Colbert, Joseph C Gaspard

  • 1College of Marine Science, University of South Florida, St. Petersburg, 33701, USA. dmann@marine.usf.edu

Journal of Comparative Physiology. A, Neuroethology, Sensory, Neural, and Behavioral Physiology
|July 8, 2005
PubMed

Insights

Florida manatees show weak auditory evoked potential (AEP) responses to tones from 4 kHz to 40 kHz. Their hearing sensitivity peaks at 150 and 600 Hz amplitude modulation rates.

Area of Science:

  • Marine biology
  • Bioacoustics
  • Auditory neuroscience

Background:

  • Understanding marine mammal hearing is crucial for conservation efforts.
  • Florida manatees (Trichechus manatus latirostris) possess unique auditory systems adapted to their aquatic environment.
  • Previous research on manatee hearing has primarily relied on behavioral audiometry.

Purpose of the Study:

  • To measure auditory evoked potential (AEP) responses in Florida manatees.
  • To characterize the manatee's modulation rate transfer function (MRTF).
  • To compare manatee auditory processing with that of other mammals.

Main Methods:

  • Auditory evoked potentials (AEPs) were recorded in response to amplitude-modulated (AM) tones.
  • Stimuli ranged from 4 kHz to 40 kHz.
  • The manatee modulation rate transfer function (MRTF) was determined by analyzing AEP responses to various AM rates.

Main Results:

  • Weak AEP responses were observed for stimuli between 4 kHz and 40 kHz.
  • The manatee MRTF showed maximal sensitivity to 150 Hz and 600 Hz AM rates.
  • Audiograms derived from AEPs underestimated behavioral hearing thresholds, likely due to electrode placement.

Conclusions:

  • Florida manatees exhibit limited auditory sensitivity in the tested frequency range based on AEPs.
  • The 600 Hz AM sensitivity suggests an intermediate auditory processing capability between terrestrial mammals and dolphins.
  • AEP-based audiograms may not accurately reflect true hearing thresholds in manatees without precise electrode placement.

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