ELASTIC MOVEMENT IN THE STRIDULATORY MECHANISM OF PURE- TONE ULTRASONIC KATYDIDS BIO 325 LECTURE #5 GUEST LECTURE: SARA J. GUTIERREZ Dita Klimas Assigned reading Montealegre-Z, F., Morris, G.K., and Mason, A.C Generation of extreme ultrasonics in rainforest katydids. J. Exp. Biol. 209, Morris G.K., Mason A.C., Wall P., Belwood J.J High ultrasonic and tremulation signals in neotropical katydids (Orthoptera: Tettigoniidae). J. Zool. London 233: Male katydids (and crickets) produce sound by rubbing their acoustically adapted forewings together this is known as wing-on-wing stridulation. A row of teeth on the underside of one wing (file) contacts a modified edge (scraper) of the other wing sending specialized sound - radiating regions (e.g., mirror) into vibration. G.K. Morris *NOTE: cricket forewings are highly symmetrical whereas most katydid forewings (as in illustration above) are not, this has implications in terms of the pure-tone stridulatory mechanism of each insect Spectral Analysis: cricket vs katydid CRICKET (resonant) KATYDID (non-resonant) G.K. Morris Montealegre et. al. (2006) Several katydid species produce pure-tone calling songs Myopophyllum speciosum Crickets make their pure-tone, one-wave one-tooth, calling songs by escapement, but katydids must use another mechanism to achieve the same result at much higher ultrasonic pure tones. Katydids making ultrasonic pure tones must keep the time taken for the scraper to travel from tooth to tooth on the file constant. This can be achieved in one of two ways: 1) pass at a constant velocity over evenly spaced teeth or 2) change velocity to offset changing tooth density. (Montealegre et al. 2006) PURE-TONE ULTRASONIC KATYDIDS: AN UNCOUPLED STRIDULATORY MECHANISM Stridulation that couples wing velocity to tooth impact rate can achieve frequencies as high as 40 kHz. The speed of wing movement coupled with inter-tooth distance can easily account for cricket carrier frequencies near 4.5 kHz, or even frequencies as high as kHz [low ultrasonics]. However coupling cannot account for carrier frequencies above 40kHz. Instead the tooth impact rate must be uncoupled from the speed of wing movement, the scraper must not move in step with the wing but how? AN ELASTIC/FLEXIBLE SCRAPER #19 Arachnoscelis n. sp. TSR1 = vs. TSR2 = fc = ~ 128kHz #7 Metrioptera sphagnorum: Lo-Freq: TSR1 = vs. TSR2 = fc = ~17.2kHz Hi-Freq: TSR1 = vs. TSR2 = fc = ~34.0kHz *** TSR1 = tooth density x closing-wing velocity *** TSR2 = tooth density x scraper velocity NOTE: values for TSR2 are representative of actual recorded carrier frequencies (fc) Montealegre et. al. (2006) Schematic cross-section of stridulatory file and scraper showing hypothetical mechanism of stridulation in extreme-frequency singers wherein tooth strike rate is uncoupled from speed of wing-movement due to elastic energy storage that propels scraper forward across the file Montealegre-Z F et al. J Exp Biol 2006;209: 2006 by The Company of Biologists Ltd Enter Metrioptera sphagnorum STOP FOR COOL EDIT SOUND CLIP Pure-tone ultrasonic Broad-band audio Ultrasonic mode averages 95 dB at 10 cm dorsal (n=20): some individuals are 100 dB Audio mode is about 6 dB less though of course it sounds much the more intense to a human listener M. Sphagnorum uses different regions of its file (Fig. 2) to produce the major pulse trains of the audio mode (C-D) and ultrasonic mode (A-B). Tooth density and width also differs see picture 6 (audio mode) and 7 (ultrasonic mode) Morris, G.K. and Pipher, R.E. (1972) BEFORE AFTER