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First published online June 15, 2007
Journal of Experimental Biology 210, 2383-2389 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.004572

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Mechanosensation and mechanical load modulate the locomotory gait of swimming C. elegans

Jeremie Korta¹, Damon A. Clark¹, Christopher V. Gabel¹, L. Mahadevan^2,3 and Aravinthan D. T. Samuel^1,*

¹ Department of Physics, Harvard University, Cambridge, MA 02138, USA
² Division of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA
³ Department of Organismic and Evolutionary Biology, Harvard University, Cambridge, MA 02138, USA

View larger version (37K): [in this window] [in a new window]   Fig. 1. The spatiotemporal dynamics of the swimming gait of C. elegans. (A) Dark-field video image of a young adult worm swimming in viscous fluid (0.5% w/w methylcellulose in NGM buffer) with its undulations within the focal plane of the microscope (also see Movie in supplementary material). Throughout this study, we used young adult worms of this size. In each video frame, custom-written machine-vision software fits a curve to the body centerline (blue line) and calculates the radius of curvature at each point along the body centerline (red line). We define a body coordinate that varies from l=0 at the head to l=L at the tail. (B) Contour plot of the spatiotemporal dynamics of about six cycles of the forward-swimming gait represented as the curvature measured at each point along the body centerline over time. Values of curvature are scaled by color, with positive (negative) curvature indicating bend in the ventral (dorsal) direction. We show the body coordinate as the fractional distance along the body length (l/L) and display data corresponding to 0.1-0.9 to avoid showing the hyperflexible movements of the worm nose and whiplike tail. We measure temporal frequency by quantifying the time period () between undulations. We measure the wave speed by quantifying the propagation of curvature down the body centerline. (C) To characterize the force and energetics of the swimming gait, we directly measured the velocity of each point along the body centerline throughout each undulation cycle. Here, we show the measurements of lateral speed, the direction orthogonal to the body centerline, at three different points along the body centerline through about six cycles of the forward-swimming gait. Positive (negative) speed indicates movement towards the ventral (dorsal) direction.

View larger version (8K): [in this window] [in a new window]   Fig. 2. Mechanical load affects the frequency but not the shape of the swimming gait. (A) The wavelength of the undulating gait of swimming worms does not vary with mechanical load. Here, we quantify the wavelength as a fraction of the total length of the body centerline. (B) The temporal frequency of the undulating gait of swimming worms drops with increasing mechanical load. (C) The mean power of the swimming gait calculated using Eqn 1 increases with swimming gait. The sublinear dependence (0.7 slope in a log-log plot) may be attributed to the drop in the temporal frequency of the swimming gait. Each measurement corresponds to data from 10-15 worms and 30-60 s of video (means ± 1 s.e.m.). Solid lines represent linear regression fits.

View larger version (13K): [in this window] [in a new window]   Fig. 3. Mechanosensory neurons affect the frequency but not the shape of the forward-swimming gait. (A) The shape of the forward swimming gait of mec-4(d) (light gray) and mec-6(u450) (dark gray) mutant worms does not vary with mechanical load. The solid line shows the line fit to wild-type data from Fig. 2A. (B) The temporal frequency of the swimming gait of mec-4(d) and mec-6(u450) mutants decreases with increasing mechanical load but is offset to higher temporal frequencies than in wild-type worms. The solid line shows the line fit to wild-type data from Fig. 2B. Each measurement in A and B corresponds to data from 10-15 worms and 30-60 s of video (means ± 1 s.e.m.). (C) The shape of the forward-swimming gait of young adult worms in 1% methylcellulose is unaffected by the mec-4(d) or mec-6(u450) mutations or by ablation of the ALM or PLM touch receptor neurons. The number of worms analyzed in each measurement is shown in parentheses. Standard deviation errors bars, typically ±5% of the mean value of each measurement, are smaller than the data points. Neither mec-4(d) or mec-6(u450) mutants are distinguishable from wild-type (P>0.01). None of the laser-ablated worms are distinguishable from the mock surgical controls, in which worms were prepared for laser surgery but not irradiated (P>0.01). (D) The temporal frequency of the swimming gait of young adult worms is significantly increased by mutation or laser ablation. Error bars indicate one standard deviation. Differences between mutant and wild-type and between laser-ablated worms and mock surgical controls are indicated at P<0.01 and at P<0.001.