Evolution of hearing - Spherical spreading of sound...

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Spherical spreading of sound http://www.sfu.ca/sonic-studio/handbook/Sound_Propagation.html Intensity = 1/r2
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Near field (particle displacement) vs. far field (pressure wave). Near field decrements at 1/r3 Far field decrements as 1/r2 (spherical spreading) http://www.asnt.org/publications/tnt/tnt2-4/4_FYI_Fig3.gif
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Cilia are found in all eukaryotes: they may have evolved from the centrioles that move cell nuclei and chromosomes during mitosis. Mitchell, 2004
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Two different types of ciliated mechanosensory organs evolved in arthropods and vertebrates. Arthropods: scolopidium Vertebrates: hair cell
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Crustacea and insects use these hairs to sense vibration, sound, and movement of their limbs (proprioception). http://www.cals.ncsu.edu/course/ent425/tutorial/tricho.gif Vibration or sound Bending of exoskeleton
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The fly antenna Kamikouci et al, 2009; Yorouzu et al., 2009 Movement of the arista activates neurons on Johnston’s organ (JO). Neurons with different properties signal “high frequency” (250 Hz) sound (near field, such as occurs by male courtship wing vibrations) or low frequency (1-2 Hz) wind or gravistatic responses.
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Parallel evolution of gravistatic and auditory receptors and circuits in flies and vertebrates.
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Scolopedia-based receptors work well for detection of near field sound (i.e. courtship sounds in two nearby Drosophila), but they do not work well in the far field. But pressure receptors will. To detect far field sound, an air-filled cavity that can be compressed works well. Tympanum does this. Also, it allows some amount of tuning by the stiffness of the membrane etc.
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Tympanic membrane-based hearing (for far field sound) evolved many times in insects Yager, 1999
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Noctuid moth ear Yager, 1999
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Auditory organ on foreleg of cricket Yager, 1999
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Tympanal organ in mantids. Tympanal organ on the midline is tuned to ultrasonic frequencies and detects bat predators. Yager, 1999
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Auditory organ in Ormia ochracea , a tachinid fly that parasitizes calling crickets. Yager, 1999 Arrows show auditory organ in an intact fly(A) and (B) a fly with the head removed. Robert et al., 1996
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Evolution of hearing - Spherical spreading of sound...

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