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First published online December 2, 2005
Journal of Experimental Biology 208, 4699-4708 (2005)
Published by The Company of Biologists 2005
doi: 10.1242/jeb.01926

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The start of phonotactic walking in the fly Ormia ochracea: a kinematic study

Andrew C. Mason^1,*, Norman Lee¹ and Michael L. Oshinsky^2,

¹ Integrative Behaviour and Neuroscience Group, Department of Life Sciences, University of Toronto at Scarborough, 1265 Military Trail, Scarborough, Ontario, Canada M1C 1A4
² Neurobiology and Behavior, Cornell University, Ithaca, NY 14853, USA

View larger version (24K): [in a new window]   Fig. 1. Calculation of two measures of the directional orientation of O. ochracea phonotactic responses. Symbols indicate the location and angular heading of a fly at each time-step along its walking trajectory. The arc represents the overall orientation of the response as an angle measured from the midline axis of the fly and a point on the walking trajectory halfway between the starting and end points of the response.

View larger version (28K): [in a new window]   Fig. 2. Initial movements of flies at the onset of walking phonotaxis are not stereotyped. Flies lunge forward with both prothoracic legs in response to a sound source directly ahead (A). In response to a lateral sound source, flies may initiate phonotaxis by stepping with either the ipsilateral (B) or contralateral (C) prothoracic legs, or with the contralateral mesothoracic leg (D).

View larger version (34K): [in a new window]   Fig. 3. Frame-by-frame sequence of walking phonotaxis in response to a lateral sound source. Time is indicated on the vertical axis (progressing downward). Top layer shows complete sequence and lower layers repeat selected frames for clarity (times of selected frames indicated in bold). The fly initiates forward translation and rotation simultaneously and walks in a tight arc until oriented towards the speaker.

View larger version (21K): [in a new window]   Fig. 4. Average responses of freely walking flies for speaker azimuth 0° (A–C, N=5 flies, 10 runs/fly) and 90° (D–F, N=7 flies, 10 runs/fly). (A,D) Mean walking path; (B,E) cumulative distance vs time from stimulus onset; (C,F) instantaneous velocity vs time from stimulus onset. Bold horizontal lines in B,C,E,F indicate stimulus duration.

View larger version (14K): [in a new window]   Fig. 5. Total walking distance in response to a single stimulus presentation with best-fit line (loess smoothing). Value are means ± S.E.M., N=16 flies, 5 runs/fly.

View larger version (24K): [in a new window]   Fig. 6. Average responses of tethered flies walking on a treadmill for speaker azimuth 0° (A–C, N=18 flies, 10 runs/fly) and 90° (B–F, N=7 flies, 10 runs/fly). (A,D) Mean walking path; (B,E) cumulative distance vs time from stimulus onset; (C,F) instantaneous velocity vs time from stimulus onset. Open symbols and gray line in C show a single response in which the fly decelerated to a complete stop following stimulus offset. Bold horizontal lines in B,C,E,F indicate stimulus duration.

View larger version (27K): [in a new window]   Fig. 7. Orientation of walking phonotaxis. Walking path for single responses of a freely walking (A) and tethered fly (B) to a speaker at 90°. Symbols indicate instantaneous heading at each time-step, with those in red indicating the duration of the stimulus. (C) Instantaneous angular heading vs time from stimulus onset for three different stimulus angles in a tethered fly. Plots are averages of 10 runs each. Vertical line indicates end of stimulus. (D) Rotational velocity vs time from stimulus onset for the same responses as shown in C. Peak rotational velocity occurs midway through the stimulus duration regardless of turn angle, and rotation decelerates before stimulus offset.

View larger version (23K): [in a new window]   Fig. 8. Characteristics of phonotactic responses as a function of source azimuth. (A) Peak (filled circles) and average (open circles) rotational velocity vary systematically with source azimuth, but saturate at large angles. (B) Angular variance of response orientation varies with source azimuth. Orientation is most variable at intermediate angles. (C) Peak translational velocity is highly variable and does not show a consistent pattern of variation with source azimuth. (D) Neither latency to peak translational velocity (filled circles) nor latency to peak rotational velocity (open circles) differs significantly for different stimulus angles. Horizontal line indicates end of stimulus duration. Peak translational velocity occurs after the end of the stimulus, whereas peak rotational velocity occurs earlier than stimulus offset. Data are means ± S.E.M. (N=7 flies, 10 runs/angle/fly).