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First published online August 31, 2007
Journal of Experimental Biology 210, 3209-3217 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.008367

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An isolated insect leg's passive recovery from dorso-ventral perturbations

Daniel M. Dudek^* and Robert J. Full

Department of Integrative Biology, University of California at Berkeley, Berkeley, CA 94720-3140, USA

View larger version (27K): [in this window] [in a new window]   Fig. 1. Experimental setup. (A) In the free-coxa preparation, the dorsal surface of Blaberus was attached using epoxy glue to 0.95 cm thick PlexiglasTM and the tarsus removed (broken outline). A servo-motor applied a dorsally directed impulse to the tibia, 1 mm from the distal tip. The free response of the leg was recorded at 1000 frames s–1 and the position of a marker 1 mm from the distal tip of the tibia was digitized. The abdomen was pulled dorsally slightly and held so that it did not interfere with the free response of the leg. The fixed-coxa preparation was identical except the leg was removed from the body and glued to the PlexiglasTM at the coxa. In all instances the femur–tibia joint was rigidly fixed by cyanoacrylate, and in half the trials the C-Tr-Fe joint was also rigidly fixed. (B) The joint axes of rotation of the distal joints are parallel with the applied impulse direction (into the page). The body coxa joint's primary axis of rotation runs medio-laterally, so it is free to rotate as a result of the dorsally directed impulse perturbation. The body–coxa joint also has secondary joint axes parallel to the applied impulse. (C) Video frames show the time sequence of the left metathoracic leg's response to an impulse perturbation. The animals's dorsal surface is towards the left of the image while anterior is towards the bottom of the image.

View larger version (15K): [in this window] [in a new window]   Fig. 2. Response of the metathoracic leg with a freely rotating body–coxa joint to an impulsive perturbation. (A) The predicted free response of a leg based on k and from dynamic oscillation experiments (Dudek and Full, 2006). Mass was assumed to be 0.1 g. (B) The actual response of a representative leg with a free body–coxa joint and fixed C-Tr-Fe and femur–tibia joints (blue) compared to the best fit line of the model (red). In all cases, the position is normalized to the peak displacement. The predicted response recovers more than 85% within the time it takes for the actual leg to recover 99%.

View larger version (14K): [in this window] [in a new window]   Fig. 3. Response of the metathoracic leg with a fixed body–coxa joint to an impulsive perturbation. (A) The predicted free response of a leg based on k and from dynamic oscillation experiments (Dudek and Full, 2006). Mass was assumed to be 0.04 g. (B) The actual response of a representative leg with a fixed body–coxa joint and fixed C-Tr-Fe and femur–tibia joints (blue) compared to the best fit line of the model (red). In all cases, the position is normalized to the peak displacement. The predicted response recovers only 50% within the time it takes for the actual leg to recover 99%.

View larger version (11K): [in this window] [in a new window]   Fig. 4. Free response recovery times. The time it takes to reach individual displacement maxima in the damped response for both the free-(dark grey) and fixed-coxa (light gray) preparations. Bars represent the mean times ± s.d. (N=10). The average swing duration for B. discoidalis running at its preferred speed is 50–60 ms. The free-coxa preparation recovers 88% of the perturbation by the second maxima and never has a third maxima with less than 95% absorption. The fixed coxa recovers 74% of the perturbation by the second maxima, 90% by the third, and never has a fourth with less than 95% absorption. In all cases the time to each point is less for the fixed-coxa legs (t-test, P<0.0001) and the time to reach 99% absorption is less than the duration of the swing phase (z-test, P<0.0001).