Peripheral frequency mis-match in the primitive ensiferan Cyphoderris monstrosa (Orthoptera: Haglidae) |
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Authors: | A C Mason G K Morris R R Hoy |
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Institution: | (1) Department of Zoology, Erindale College, 3359 Mississauga Rd., Mississauga, Ontario, Canada L5L 1C6, CA;(2) Department of Neurobiology and Behavior, SG Mudd Hall, Cornell University, Ithaca NY 14853, USA, US |
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Abstract: | Peripheral auditory frequency tuning in the ensiferan insect Cyphoderris monstrosa (Orthoptera: Haglidae) was examined by comparing tympanal vibrations and primary auditory receptor responses. In this species
there is a mis-match between the frequency of maximal auditory sensitivity and the frequency content of the species' acoustic
signals. The mis-match is not a function of the mechanical properties of the tympanum, but is evident at the level of primary
receptors. There are two classes of primary receptors: low-tuned and broadly tuned. Differences in the absolute sensitivity
of the two receptor types at the male song frequency would allow the auditory system to discriminate intraspecific signals
from sounds containing lower frequencies. Comparisons of tympanal and receptor tuning indicated that the sensitivity of the
broadly tuned receptors did not differ from that of the tympanum, while low-tuned receptors had significantly narrower frequency
tuning. The results suggest that the limited specialization for the encoding of intraspecific signals in the auditory system
of C. monstrosa is a primitive rather than a degenerate condition. The limited specialization of C. monstrosa may reflect the evolutionary origin of communication-related hearing from a generalized precursor through the addition of
peripheral adaptations (tympana, additional receptors) to enhance frequency sensitivity and discrimination.
Accepted: 13 March 1999 |
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Keywords: | Auditory physiology Insect Frequency discrimination Evolution Song recognition |
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