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First published online March 21, 2005
Journal of Experimental Biology 208, 1219-1237 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01526

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The mechanics of sound production in Panacanthus pallicornis (Orthoptera: Tettigoniidae: Conocephalinae): the stridulatory motor patterns

Fernando Montealegre-Z^1,* and Andrew C. Mason²

¹ Department of Zoology, University of Toronto at Mississauga, 3359 Mississauga Road, Mississauga, Ontario, Canada, L5L 1C6
² Integrative Behaviour and Neuroscience Group, Department of Life Sciences, University of Toronto at Scarborough, 1265 Military Trail, Scarborough, Ontario, Canada, M1C 1A4

View larger version (79K): [in a new window]   Fig. 1. Tegminal structure. Left (A) and right (B) tegmina. Marked regions indicate areas of maximal vibration in particle displacement studies of the right tegmen, and homologous regions on the left tegmen. Scale bar, 6 mm. Regions 1, 3 and 4 were experimentally found only for the right tegmen, but homologised for the left. The rest were chosen according to the thickness of the wing and used in complementary studies of wing vibration (data not published here). Venation nomenclature and vein identification were adopted from Desutter-Grandcolas (2003), and when explicit names or locations of some veins were not provided, we inferred them.

View larger version (170K): [in a new window]   Fig. 2. Scanning electron micrographs of the stridulatory file. (A) Proximal end of the file showing variation in inter-tooth distances towards the costal margin; scale bar, 231 µm. (B) Detail of teeth from the mid portion of the file in lateral view showing teeth asymmetry and orientation angle; scale bar, 100 µm. (C) Mid portion of the file as seen in dorsal view; scale bar, 231 µm. (D) Entire file showing its curvature and variation in width; scale bar, 1.36 mm.

View larger version (18K): [in a new window]   Fig. 3. Diagram of the setup for measuring the natural frequency of vibration fo of isolated wings. A dissected segment of file (or scraper) was mounted on a probe held in a micromanipulator. This was used to simulated single file-tooth impacts and generate free vibration in the wing. Wing vibration was measured directly using a laser vibrometer and radiated sound was recorded using a probe microphone.

View larger version (76K): [in a new window]   Fig. 4. Calling song analysis. (A) Oscillogram of a single P. pallicornis song; scale bar, 10 ms. (B) Detail of waveform shown in A; scale bar, 0.5 ms. (C) Power spectrum of the song in shown in A. (D) Spectrograms of two different specimens (note inter-individual variation of call). While the overall spectrum (C) is noisy, spectrograms (D) reveal a segment in the middle of the call with clearer tonality and harmonic structure.

View larger version (73K): [in a new window]   Fig. 5. Scraper morphology. (A) Scraper region of the right tegmen, viewed dorsally, with adjacent veins and cells indicated. (B) Cross section of the scraper-bearing region of the right tegmen though the area indicated in B (blue broken line); scale bar, 1 mm. Dotted circle indicates the region shown in C. (C) A scanning electron micrograph of the edge of the right tegmen at the location of the scraper. Labels refer to structures described in the text; scale bar, 100 µm.

View larger version (26K): [in a new window]   Fig. 6. Distribution of teeth on the stridulatory file. (A) Plot of the inter-tooth distances over the length of the file for six specimens of P. pallicornis, each indicated with a different colour and symbol. Inter-tooth distances increase towards the basal end of the file (i.e. where the scraper contacts the last teeth during the closing stroke), but this increase is not smooth. (B) Plot of the cumulative number of teeth vs total distance along the file of five specimens (each shown in different colour). This indicates that the inter-tooth distance gradually increases basally, and that half of the total numbers of teeth are located in the anal one third of the file. (C) Inter-tooth distances of five Panacanthus spp. Trend lines are Lowess curve fits. Second degree polynomial regressions of inter-tooth distance against tooth number showed lower variability of tooth spacing in species using sustained pulses [P. cuspidatus, r2=0.95 (red outline) and P. pallicornis r2=0.87 (blue)]. Tooth spacing was more variable in species using transient pulses with broad band spectrum [P. gibbosus, r2=0.75 (black), P. intensus, r2=0.74 (green), P. varius, r2=0.02 (purple)].

View larger version (73K): [in a new window]   Fig. 7. Wing movements during sound production recorded simultaneously with two different methods: high-speed video (top) and optical position detector (bottom). Four frames from one complete wing stroke are shown. Each frame is accompanied by an oscillogram of the sound (blue) and simultaneous trace of wing position vs time (red). Vertical broken lines (red) indicate the position of the scraper in the video frame. In the simultaneous sound and wing position traces, the vertical broken line indicates the time corresponding to the video frame. (A) Maximal opening of wings, just prior to engagement of file and scraper and beginning of sound production. (B) The scraper contacts the first teeth of the file and the first sound waves are generated. Note decrease in the slope of wing position (red trace) when the scraper contacts the first teeth (green broken arrow). (C) The scraper crossing the middle portion of the file, maximum amplitude of the song pulse, increasing slope of wing position trace. (D) The scraper contacts the last few teeth of the file and comes to rest with the end of the sound pulse.

View larger version (33K): [in a new window]   Fig. 8. Sound oscillograms and wing movements as recorded with the optical position detector. (A) Five consecutive songs (black) with their corresponding wing position trace (red); scale bar, 0.5 s. (B) Enlargement of one pulse of the sequence shown in A; scale bar, 20 ms. (C) Further enlargement of a segment of the pulse shown in B. Ripples in the wing position trace match sound waves; scale bar, 1 ms. (D) Velocity of wing closing, calculated from frame-by-frame analysis of high-speed video. Results for one song from each of four individuals are shown (symbols) along with a Lowess curve fit to the data (blue). (E) Velocity of wing closing, calculated from the wing movement trace of the position detector. Wing velocity traces for four songs from the same specimen are plotted (black) and line fitted to the average using the Lowess curve fit (blue).

View larger version (45K): [in a new window]   Fig. 9. Removal of mirror regions. Analysis of calls from one individual before (A) and after (B) removal of the membranes of Areas 1, 3 and 4 of the right tegmen. Oscillograms are shown in the left, power spectra in the middle and spectrograms on the right. Red arrows indicate the same frequency in the spectral displays (middle and right). After removal of Areas 1, 3 and 4, there was a decrease in the relative intensity of the fundamental and an increase in harmonic frequency components.

View larger version (119K): [in a new window]   Fig. 10. Effects of loading the left tegmen. Spectrogram of songs of the same specimen intact (A), after loading the the acoustic regions of the left tegmen (B), following removal of the latex from the left tegmen (C) and after loading the mirror of the right tegmen (D). Red arrows in A–C indicate the same frequency. Harmonic components decreased in frequency when the left tegmen was loaded and recovered following removal of the latex. Loading of the right tegmen eliminated the harmonic structure of the call. A segment of the oscillogram at high resolution in every case is presented below each panel; scale bar, 60 ms.

View larger version (58K): [in a new window]   Fig. 11. Effect of removing teeth from the stridulatory file. (A) Sound oscillogram (blue) and wing position (red) of an intact specimen. (B) Sonogram of the sound presented in A, along with the instantaneous velocity of wing movement (blue). Note the gradual and constant increase in velocity during the region with strong harmonics. (C) Sound and wing movement of the same specimen after ablation of teeth in three different parts of the file. First gap corresponds to the removal of 11 teeth between teeth 125 to 135 (gap=0.29 mm); the second gap results from absence of 7 teeth between tooth 142 and 148 (gap=0.17 mm) and the last gap from removal of 7 teeth between 184 and 190 (gap=0.21 mm). Note the abrupt changes in wing movement when the scraper encounters these gaps. The number of sound produced in segments between the gaps in the oscillogram matches the number of teeth in the intact regions of the file. (D) Sonogram of the sound shown in C, including the wing velocity (blue). Wing velocity is more variable than when the file is intact (B) with abrupt changes in velocity corresponding to gaps in the file. Scale bars in A and C refer to wing position traces.

View larger version (30K): [in a new window]   Fig. 12. Morphological measurements of the stridulatory file compared with sound characteristics of P.pallicornis (specimen P473). (A) File tooth distribution (B) Graph of the cycle-by-cycle frequency vs time of the song pulse shown in C. (C) Oscillogram the song pulse after low-pass filtering (7.5 kHz, see Materials and methods) high-frequency components.

View larger version (69K): [in a new window]   Fig. 13. (A) Cycle-by-cycle frequency analysis of a calling song. The fundamental frequency is more constant in the middle portion of the song, corresponding to the strong harmonics evident in the spectrogram of the same song (B). The blue trace represents the instantaneous velocity of the wing, calculated from the wing movement recordings. (C) Plot of predicted wing velocity (triangles, green line) for the song shown in A and B, and measured wing velocity (circles, blue line) for this song and three others from the same individual. Predicted wing velocity is calculated from the cycle-by-cycle frequency data and the measured distances between adjacent file teeth in this specimen. For each cycle of sound output, we obtained the period and calculated the wing velocity required for the scraper to traverse the corresponding inter-tooth gap in that time. This indicates the instantaneous wing velocity required for tooth-scraper impacts to occur at the same phase in every cycle of sound output. The blue and green lines are Lowess curve fits to the data. The harmonic portion of the song occurs when the actual wing velocity most closely approaches the predicted velocity required for consistent phasing of tooth impacts.

View larger version (16K): [in a new window]   Fig. 14. Resonances of the forewings. (A) Free vibration of the right tegmen as recorded from region 4 with a probe microphone (red outline) and with a laser vibrometer (blue outline). Free vibration of the right (B) and left (C) wing of P. pallicornis recorded by laser vibrometer over region 1 of both wings; scale bar, 2 ms. Vibrations were induced by simulating single file-tooth/scraper impacts in dissected wings. The Q values presented above each oscillogram are means of four specimens. Power spectral analysis is shown below each oscillogram, with specimens shown in different colour outlines.

View larger version (34K): [in a new window]   Fig. 15. Model of scraper–file interactions and their relation to sound. (A) Hypothetical file segment and scraper region. Note the increments in inter-tooth distances (in the direction of scraper movement) indicated with blue dotted lines and letters; the structures of the scraper involved are also labelled. The sound cycle, shown below, was generated when the scraper was released from T2 (tooth 2) and crossed the region with distance D1. Note that the scraper has been released and is moving forwards, travelling over D1 to find the following tooth (T3). HPZ and LPZ, higher and lower pressure zones of the sound wave, respectively. (B) The scraper hits T3, generating a reaction of the system at its natural frequency ( 5 kHz for P. pallicornis). The oscillatory reaction is shown in the diagram with a red outline (half a cycle), which is added before the previous cycle, indicated in A, decays. The impact will also generate a vibration of high frequency (see Bennet-Clark and Bailey, 2002), represented with a red asterisk but not indicated in the oscillation of the diagram. The scraper is temporarily trapped by T3 but, as the forewings continue in motion, the scraper regions bend upwards. In this model, the initial deflection of the oscillator is upward, to generate the higher pressure zone (maximal amplitude of the sound cycle, see A); scale bar, 0.11 ms. (C) The motion of the wings causes the scraper to dislodge while the first half of the oscillation is completed. (D) The distorted adjacent membranes temporarily recover their original shape, passing through equilibrium. The adjacent membranes and the rest of the oscillator of the right tegmen continue their vibration downward to generate lower pressure zone, completing the second half of the cycle (red outline). The scraper completely dislodges from T3, generating a click sound also of high frequency (blue asterisk), and travels over D2. Scale bar, 0.22 ms. (E) The scraper travels D2 and strikes T4 before the previous oscillation decays; this action repeats over and over. Note that the time spent by the scraper to go from one tooth to the next is equal to the period of 5 kHz (0.22 ms 1/5 kHz).