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First published online December 1, 2006
Journal of Experimental Biology 209, 4923-4937 (2006)
Published by The Company of Biologists 2006
doi: 10.1242/jeb.02608

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Generation of extreme ultrasonics in rainforest katydids

Fernando Montealegre-Z^1,*, Glenn K. Morris² and Andrew C. Mason¹

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

View larger version (31K): [in this window] [in a new window]   Fig. 1. Features of Arachnoscelis n. sp. (A) Male adult insect on human arm (photo by D. E. Klimas); scale bar, 15 mm. (B) One calling song of two pulse trains, more typically one train; scale bar, 20 ms. (C) High resolution of a mid-train pulse; scale bar, 100 µs. (D) Smoothed power spectrum of calling song. (E) ZC analysis of the pulse in D. Note how the frequency drops for the driven cycles (black arrows), indicating a decrease in velocity, then increases during decay (red arrow), suggesting that the scraper has disengaged from the file (event indicated by red asterisks); note that the file's resonant frequency is normally higher than that of the calling song. Blue arrows show the free decay of the pulse. Q, quality factor.

View larger version (43K): [in this window] [in a new window]   Fig. 2. Four successive frames from high-speed video relate closing wing positions to the pulse train of Arachnoscelis n. sp. Insect faces to the right. The anal margin of the overlying (file-bearing) left wing is marked by a red arrow; coloured broken lines match picture and wing velocities to the oscillogram. The wings develop a velocity before each production of a pulse (calculated CWV below frame) and then become almost still over the interval of pulse generation; scale bar, 5 ms. (A) CWV is at 7.1 mm s-1; scale bar, 0.5 mm. (B) During the production of the first pulse (compare A and B) there is no detectable movement of the wings and the CWV drops to zero. (C) The wings close further, giving a CWV of 14.5 mm s-1. (D) Next pulse is produced, again without measurable displacement of the wings. Association of motionless wing intervals with sound pulses implies scraper movement.

View larger version (35K): [in this window] [in a new window]   Fig. 3. File morphology of Arachnoscelis n. sp. (A) Scanning electron microphotograph shows the stridulatory file atop its transverse swollen vein. The long white arrow gives direction of scraper travel. Scale bar, 0.2 mm. (B) Inter-tooth distances for two specimens, the smaller animal below. Broken blue lines show the functional region (basal half) of the file as determined from HSV recordings of the 2003 specimen, which makes 4-5 pulses song-1. Sound recordings of the 1966 specimen suggest that some specimens use a larger file region, which implies the production of a larger pulse train (more pulses), as shown in Fig. 1B.

View larger version (50K): [in this window] [in a new window]   Fig. 4. Four successive frames from high-speed video (scale bar 3 mm) showing tegminal positions within the time course of the (closing) AM pulse pattern in Myopophyllum n. sp. The insect is oriented upward. The position of the right wing scraper region, visible through semitransparent wing cells of the left, is marked by a red arrow; coloured broken lines show where in the oscillogram time course the frame was obtained. (A) CW velocities are associated with each frame: the wings lose velocity before the production of a pulse. Scale bar, 2 ms. (B) There is a conspicuous displacement of the wings during the production of a pulse and the CWV increases to 142 mm s-1. (C) The wings close again more slowly during the silent interpulse interval and CWV drops to 82 mm s-1; during this time interval the scraper is relocated. (D) The new pulse is produced with a conspicuous displacement of the wings; CWV increases to 118 mm s-1.

View larger version (53K): [in this window] [in a new window]   Fig. 5. Four successive frames from high-speed video (scale bar 3 mm) showing tegminal positions within the time course of the (closing) AM pulse pattern in Eubliastes aethiops. Latero-posterior view (right side of the insect). The position of the scraper over the file is marked by a red arrow; coloured broken lines show where in the oscillogram time course the frame was obtained. (A) CWV values are associated with each frame: the wings lose velocity before the production of a pulse. Scale bar, 10 ms. (B) As for Myopophyllum sp. n., there was a conspicuous displacement of the wings during the production of a pulse and the CWV increases to 166.1 mm s-1. (C) For the final pulse of the train, the wings close again more slowly during the silent interpulse interval and CWV drops to 134.3 mm s-1, and increases again during the pulse to 169.8 mm s-1 (D). The movement of the scraper ends close to the basal part of the file.

View larger version (16K): [in this window] [in a new window]   Fig. 6. File morphology and sound quality of two species of katydid using sustained pure tones. (A,D) Intertooth intervals plotted in their natural sequence on the file. (B,E) Zero-Crossing analysis of the pulse shown in C and F; red arrows indicate increments in frequency associated with scraper-file disengagement. (C,F) Sound pulse waveform.

View larger version (12K): [in this window] [in a new window]   Fig. 7. Verification of our method of estimating closing wing velocity from oscillograms (especially for species where specimens were not available for HSV). Regression of known on estimated values indicates good agreement (see text).

View larger version (20K): [in this window] [in a new window]   Fig. 8. (A) Analysis of relationship between song frequency and wing speed by ANCOVA with wing speed as the continuous variable and group membership (high vs low frequency). Closed symbols represent high-frequency singers (>40 kHz); open symbols, low-frequency singers (<40 kHz). (B) Same analysis using average TSR as independent variable.

View larger version (20K): [in this window] [in a new window]   Fig. 9. Scraper profiles and their association with two types of resonant stridulatory mechanism: long-pulse and short-pulse. Each transverse section is taken normal to the scraper edge. (A) Two species producing pure-tone pulses below 40 kHz. (B) Two species producing extreme ultrasonics (>60 kHz) as short-spaced pulse trains. Note the distinctive morphology proximad of the scraper (red areas): the very modest extent of thinner (presumably more flexible) wing areas in A compared with their elaboration relative to increasingly massive veins in B. A1, A2, A3 indicate anal veins.

View larger version (37K): [in this window] [in a new window]   Fig. 10. Schematic cross-section of stridulatory file and scraper (based on anatomy of Arachnoscelis n. sp.) showing hypothetical mechanism of stridulation in extreme-frequency singers. (A) Different degrees of deformation the scraper may undergo while pausing behind a tooth in advance of pulse production. (B) With enough bending, the scraper's shape allows release, and it springs forward along a series of teeth lodging at the last tooth of the series (blue asterisk). Pulse-driven oscillations (one per tooth) indicated with broken lines, contacted teeth with red asterisks. Decay oscillations indicated by dotted red arrows.