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First published online December 26, 2008
Journal of Experimental Biology 212, 194-209 (2009)
Published by The Company of Biologists 2009
doi: 10.1242/jeb.018317
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Straight walking and turning on a slippery surface

Matthias Gruhn*, Lyuba Zehl and Ansgar Büschges

Department of Animal Physiology, Zoological Institute, University of Cologne, Weyertal 119, 50923 Cologne, Germany


Figure 1
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  		Fig. 1. (A) Overlay of all tracked frames from a single walking sequence. Tracked dots mark the distal ends of the femora and the tibiae of all legs, the head is pointing to the right. The animal was performing a left turn in the depicted sequence. (B) Schematic drawing of the stick insect with the points tracked. x-values always denote points along the axis of the animal whereas y-values mark points perpendicular to the animal. The x0-value was always set at the level of the coxae for each leg to give a clear reference point. As an example for the determination of the vector for step length and direction, the right middle leg is drawn in two arbitrary positions, one anterior extreme position (ML–AEP) and one posterior extreme position (ML–PEP). The vectors for all steps connecting the two positions, normalized to the origin in the AEP, gave direction in deg. and step length in mm. The 0–180 deg. axis was always parallel to the body axis and crossed the AEP, 270 deg. always points away perpendicularly. ML, middle leg; FL, front leg; HL, hind leg.

 

Figure 2
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  		Fig. 2. Straight walking of the intact stick insect on the slippery surface. (A) Pattern of straight walking stepping sequence on the slippery surface. The black bars mark the stance, the white gaps mark the swing phases for the six legs. From top to bottom; left front leg (lFL), left middle leg (lML), left hind leg (lHL) and right front leg (rFL), right middle leg (rML) and right hind leg (rHL). (B) Schematic drawing of a stick insect with the mean anterior extreme position (AEP) and posterior extreme position (PEP) values (and s.d.) for the straight walking animal. Dark gray marks the values for the averaged steps from the left and right side plotted separately, black marks the values for all pooled, averaged and mirror imaged data points. The light gray lines mark the respective x0-value for the middle and hind legs. (C) Mean vectors of stance phase movement drawn to the mean step length as calculated between AEP and PEP. (D) Step-to-step variability in angle and length of all stance phase movement vectors for the front, middle and hind legs. All vectors of the right side legs were mirror imaged to show only left side-stepping.

 

Figure 3
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  		Fig. 3. Turning in the intact stick insect on the slippery surface. (Ai-iii) Three typical walking sequences with the anterior extreme position (AEP) and posterior extreme position (PEP) connected by arrows for one straight walking sequence (Ai, black), and two curve walking sequences (Aii and Aiii) of differing steepness. Red marks inside legs, yellow marks outside legs. (B) Schematic drawing of a stick insect with the mean AEP and PEP values (and s.d.) for the straight walking and turning animal. Red marks the values for the averaged steps for the inside leg, dark yellow for the outside legs and black for the straight stepping legs (from Fig. 2). The light gray lines mark the respective x0-value for the middle (ML) and hind (HL) legs. (C) Mean vectors of stance phase movement of the inside (red), outside (dark yellow) and straight stepping (black) left legs, drawn to the mean step length as calculated between AEP and PEP. (D,E) Step-to-step variability in angle and length of all stance phase movement vectors for the inside (D, red) and outside (E, yellow) front, middle and hind legs (iFL, inside front legs; iML, inside middle legs; oFL, outside front legs; oML, outside middle legs). All vectors of the right side legs were again mirror imaged to show only left side stepping; coloring is the same as in A.

 

Figure 4
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  		Fig. 4. Turning vs straight stepping in the intact stick insect. (A) Mean step length of front, middle and hind legs during inside turning (red, in), straight stepping (black, str) and outside leg stepping (dark yellow, out) in mm. (B) Mean angles of the stance phase movement vector between AEP and PEP in front, middle and hind legs under the three behavioral conditions, given in deg. Labeling is the same as in A. A 90 deg. angle means a movement perpendicular to and towards the body, 180 deg. a front-to-back movement parallel to the body. Significance levels are: **P<0.01; ***P<0.001; n.s., not significant. FL, front legs; ML, middle legs; HL, hind legs.

 

Figure 5
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  		Fig. 5. Turning and straight stepping in the two-leg preparation (A) Schematic drawing of a stick insect with the mean anterior extreme position (AEP) and posterior extreme position (PEP) values (and s.d.) for the straight walking and turning two-legged-preparation (2L). Red marks the values for the averaged steps for the inside leg, dark yellow for the outside legs and black for the straight stepping legs. Pink (inside), light yellow (outside) and gray (straight walking) mark the connections between AEP and PEP in the respective legs of the intact animal. (Ai) 2L–front leg preparation (2L–FL). (Aii) 2L–middle leg preparation (2L–ML). (B)Mean vectors of stance phase movement of the inside (red), outside (dark yellow) and straight stepping (black) left legs, drawn to the mean step length as calculated between AEP and PEP for the front and middle legs. (C,D)Step-to-step variability in angle and length of all stance phase movement vectors for the inside (C, red) and outside (D, dark yellow) front and middle legs. All vectors of the right side legs were again mirror imaged to show only left side stepping; coloring is the same as in Figs 3 and 4. (E)Mean step length of front and middle leg 2L-preparation during inside turning (red, in), straight stepping (black, str) and outside leg stepping (dark yellow, out) in mm. (F)Mean angles of the stance phase movement vector between AEP and PEP in the front and middle legs under the three behavioral conditions, given in deg. Coloring is the same as in E. Significance levels in E and F are: **P<0.01; ***P<0.001; n.s., not significant. iFL, inside front legs; iML, inside middle legs; oFL, outside front legs; oML, outside middle legs.

 

Figure 6
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  		Fig. 6. Turning in the single-leg preparation. (A) Schematic drawings of a stick insect segment with the mean anterior extreme position (AEP) and posterior extreme position (PEP) values (and s.d.) for the turning 1L-preparation in the inside (Ai) and outside (Aii) front leg, and the inside (Aiii) and outside (Aiv) middle leg. The darkly colored traces with error bars mark the single-leg preparations, the lighter shaded red and yellow bars mark the connection between mean AEP and PEP in the 2L (red) and the intact preparations (light red or yellow) for comparison (B) Mean vectors of stance phase movement of the inside (red) and outside (yellow) stepping left legs, drawn to the mean step length as calculated between AEP and PEP for the single front and middle legs. (C,D) Step-to-step variability in angle and length of all stance phase movement vectors for the inside (C, red) and outside (D, dark yellow) front and middle legs (iFL, inside front legs; iML, inside middle legs; oFL, outside front legs; oML, outside middle legs). All vectors of the right side legs were again mirror imaged to show only left side stepping; coloring is the same as in Figs 3, 4 and 5. (E) Mean step length of front and middle leg 1L-preparation during inside turning (red, in), and outside leg stepping (dark yellow, out) in mm. (F) Mean angles of the stance phase movement vector between AEP and PEP in the front and middle legs under the two behavioral conditions, given in deg. Coloring is the same in E. Significance levels in E and F are: ***P<0.001; n.s., not significant.

 

Figure 7
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  		Fig. 7. Variability of the anterior extreme position (AEP) and posterior extreme position (PEP) during inside stepping in the middle leg. (A–C) Intact animal, (D–F) 2L-preparation and (G–I) 1L-preparation. A,D,G: Scatter plots of the AEP and PEP of the middle inside leg in the intact, the 2L- and the 1L-preparation. B,C,E,F,H,I: Histograms of the frequency of the occurrence of AEP and PEP x- (B,E,H) and y-positions (C,F,I) in the inside middle leg of the intact animal, the 2L-preparation and the 1L-preparation. AEP in green; PEP in orange. All positions are given in mm.

 

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© The Company of Biologists Ltd 2009