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First published online October 5, 2006
Journal of Experimental Biology 209, 4115-4128 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02460
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Tuning the drum: the mechanical basis for frequency discrimination in a Mediterranean cicada

Jérôme Sueur1,*, James F. C. Windmill2 and Daniel Robert2

1 NAMC-CNRS UMR 8620, Bât. 446, Université Paris XI, 91405 Orsay Cedex, France
2 School of Biological Sciences, University of Bristol, Woodland Road, Bristol, BS8 1UG, UK


Figure 1
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  		Fig. 1. Male Cicadatra atra emitting a calling song in a typical upside-down position. The white arrow on the male shows the localization of the auditory sensory organ. Scale=5 mm. Picture by Stéphane Puissant/OPIE-LR.

 

Figure 2
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  		Fig. 2. Posterior view of female left tympanum and male right tympanum with close-up on the ridge. The membrane and the ridge are shown on male tympanum, the red dots indicating the laser positions where frequency measurements were made. X and Y, respectively, indicate the apex and the base of the ridge. Scale=0.5 mm.

 

Figure 3
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  		Fig. 3. Calling song of Cicadatra atra. (A) Spectra of four distinct males (grey lines) and their mean (black line). (B) Oscillogram and spectrogram corresponding to the zone delimited by the vertical red lines on the bottom oscillogram. (C) Oscillogram showing successive calls. Red lines show the part of the song enlarged in B.

 

Figure 4
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  		Fig. 4. Deflection shapes of a female right tympanal membrane. TM was stimulated with a FM sweep signal. The oscillations are shown for four different driving frequencies (5, 10, 15, 20 kHz) at four different phases (0, 90, 180, 270°) along the oscillation cycle. For 10 kHz, the dominant frequency of male calling song, deflections are shown as profiles, as if looking at the tympanum from its side. Deflections are expressed as displacement gain following the colour scale. Red indicates outward tympanal deflections and green inward tympanal deflections. Note the difference in scale for each driving frequency. Orientation is indicated by a 3D space reference (D, dorsal; V, ventral; P, posterior; A, anterior; L, left; R, right). The horizontal black arrow indicates the direction of wave propagation. The ridge is visible as a black elongated teardrop (blue arrow) on the scan map.

 

Figure 5
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  		Fig. 5. Deflection shapes of a male left tympanal membrane. TM was stimulated with a FM sweep signal (0–30 kHz). The horizontal arrow indicates the direction of wave propagation. See Fig. 4 for details.

 

Figure 6
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  		Fig. 6. Deflection shapes of a male left tympanal ridge as revealed by high resolution scanning. Stimulation was done with a FM sweep stimulus. The horizontal arrow indicates the direction of wave propagation. See Fig. 4 for details.

 

Figure 7
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  		Fig. 7. Deflection shapes of a male left tympanal ridge and female right tympanal ridge. TM was stimulated with a natural male calling song. Deflections are shown for a 10 kHz frequency sine wave (calling song dominant frequency). Horizontal arrows indicate the direction of wave propagation. Note the difference in scale range between male and female. See Fig. 4 for details.

 

Figure 8
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  		Fig. 8. Phase response along the ridge (TR). The phase response shows an increasing lag with both frequency and distance along the ridge. The phase lag increases to –300° for females and to –900° for males. X=TR apex, Y=TR base (see Fig. 2).

 

Figure 9
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  		Fig. 9. Envelopes of mechanical deflections along the tympanal ridge. Top: for a 10 kHz driving frequency (calling song dominant frequency), deflections are shown for phase increments of 10° in the full oscillation cycle. Minimal and maximal values are plotted in red. Bottom: minimal and maximal deflection shapes for different driving frequencies: 5 kHz (black), 10 kHz (red), 15 kHz (green), 20 kHz (blue). Coloured dots indicate the position along the ridge where the deflection envelope is maximum for the frequency coding by colour. X, apex of the TR; Y, base of the TR.

 

Figure 10
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  		Fig. 10. Frequency response of the ridge when stimulated with a FM sweep stimulus. Frequency spectra of ridge resonance were computed at each point of a 35-point line scan from the apex of the ridge to its base. Spectra were then plotted successively on a density plot ranging from 0 to –50 dB.

 

Figure 11
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  		Fig. 11. Frequency of maximal mechanical response measured along the ridge, from apex to base, in response to FM sweep stimulus. Grey area corresponds to the frequency band containing 50% of calling song spectral energy. Values are means ± s.d. for 9 males (blue) and 6 females (red).

 

Figure 12
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  		Fig. 12. Travelling wave parameters of the ridge: (A) Phase difference, (B) travel time, (C) wave velocity, (D) wavelength. Values are means ± s.d. for 9 males and 6 females.

 

Figure 13
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  		Fig. 13. Oscillations of the tympanum ridge after the broadcast of an intense short click. Oscillations are shown for one female and one male at three positions along the ridge: apex, middle and base. Note the difference in amplitude and period of the oscillations.

 

Figure 14
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  		Fig. 14. Frequency response of the ridge from apex to base, stimulated with clicks. Grey area corresponds to 50% of calling song spectral energy. Values are means ± s.d. for 6 males (blue) and 3 females (red).

 

Figure 15
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  		Fig. 15. Response velocity of the tympanal membrane at 11.7 kHz as a function of a continuous increase in forcing. Sound pressure was linearly increased from 1 mPa to 30 mPa in the time span of 5 s. Black curve: vibration velocity measured on the ridge (between the apex and the base). Green curve: time profile of sound stimulus.

 

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© The Company of Biologists Ltd 2006