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First published online October 19, 2007
Journal of Experimental Biology 210, 3862-3872 (2007)
Published by The Company of Biologists 2007
doi: 10.1242/jeb.009050

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Effects of perch diameter and incline on the kinematics, performance and modes of arboreal locomotion of corn snakes (Elaphe guttata)

Henry C. Astley^* and Bruce C. Jayne

Department of Biological Sciences, University of Cincinnati, PO Box 210006, Cincinnati, OH 45221-0006, USA

View larger version (4K): [in this window] [in a new window]   Fig. 1. Methods for kinematic analysis. Anterior is to the right. (A) White dots indicate the locations of mid-dorsal paint marks that were digitized. xs and dcr denote the length of the region of static contact and the distance between adjacent crossings, respectively. (B) The convention for measuring crossing angles, cr. A helical loop around the perch occurs between the fourth and sixth crossing regions.

View larger version (17K): [in this window] [in a new window]   Fig. 2. The effects of perch incline on locomotor mode and movement. The tracings are from dorsal view videos of a corn snake (SVL=102 cm, mass=400 g, 4.1 cm perch) and show seven consecutive images at equal time intervals within a single cycle of concertina locomotion (A,B). The downhill sequence (C) is for the same total time as A. The shaded areas indicate static contact with the perch. (A) Uphill 90°. (B) Horizontal. (C) Downhill 90°. The times between successive images of B and C are 0.53 s, and 0.7 s for A.

View larger version (12K): [in this window] [in a new window]   Fig. 3. The effect of incline on forward (x) and lateral (y) displacement of a single longitudinal point over time. All graphs are of a mid-body point on the same individual moving on a 4.1 cm perch and equivalent tunnel width (8.1 cm). Twice as much time is shown for the perches (B–D) compared to the tunnel (A). The arrows in B indicate backwards slipping. A, B and C illustrate approximately two, one and two complete cycles, respectively, and D displays non-cyclic downward sliding. (A) Tunnel. (B) Uphill 90° perch. (C) Horizontal perch. (D) Downhill 90° perch.

View larger version (19K): [in this window] [in a new window]   Fig. 4. Dorsal views of the paths traveled by different longitudinal points on a single snake (SVL=102 cm, mass=400 g) in tunnels and on perches at three inclines. Broken lines indicate when points were obscured by the perch. All perches had a diameter of 1.6 cm, and the tunnel had an equivalent width (5.6 cm). The longitudinal points are numbered from anterior to posterior (head=1) at 20-vertebrae intervals. (A) Tunnel. (B) Uphill 90° perch. (C) Horizontal perch. (D) Downhill 90° perch. For all perches (B–D), symbols are placed every 0.5 s. For the tunnel, symbols are placed every 0.03 s. Note that the entire body of the snake follows a nearly identical path in B and C but not in A and D.

View larger version (17K): [in this window] [in a new window]   Fig. 5. Mean values (± s.e.m) of kinematic variables. (A) Cycle duration, tcycle. (B) Percent of time in static contact, %stat. (C) Forward displacement per cycle, x. (D) Mean forward velocity, Vx. (E) Forward velocity of crossing points, Vx,cr. The downhill data were omitted from A–C because snakes did not stop periodically. Values for the largest two tunnel widths in A, B and C are only from the single individual who performed concertina locomotion, whereas D includes values from two additional individuals that performed lateral undulation.

View larger version (14K): [in this window] [in a new window]   Fig. 6. Mean values (± s.e.m.) of kinematic variables. (A) Maximum x length of moving zone, xm. (B) Maximum x length of static zone, xs. (C) Maximum number of crossings, Ncr,max. (D) Change in the number of crossings during a cycle, Ncr. (E) Mean angle of crossings, cr. The downhill data were omitted from A and B because snakes did not stop periodically.

View larger version (14K): [in this window] [in a new window]   Fig. 7. The effects of perches versus tunnels and width on posture of a corn snake (SVL=102 cm, mass=400 g). (A) Horizontal perches of all seven diameters (1.6, 2.9, 4.1, 5.7, 8.9, 15.9 and 21.0 cm). (B) Horizontal tunnels of all seven corresponding widths (5.6, 6.9, 8.1, 9.7, 12.9, 19.9 and 25.0 cm). The shaded areas indicate the regions of static contact with the surface. In the 19.9 and 25.0 cm tunnels, only a single snake moved using concertina locomotion, and in the 25.0 cm tunnel it did so without any crossing regions. All images are for the time within a cycle when the region of static contact is longest. Videos of locomotion described in this paper can be found at http://bioweb.ad.uc.edu/faculty/jayne/videos.htm.

View larger version (11K): [in this window] [in a new window]   Fig. 8. Modes of sideways toppling failure. (A) Toppling by pivoting over a static contact point. (B) Toppling by slipping on the perch surface. The maximum angular deviations from vertical before toppling and the stable regions on the perches are green. For both toppling failures, the red image indicates the rotational movement about the axis indicated by +. (C) The angle, , relative to vertical at which pivot toppling (A) occurs as a function of animal shape (h L–1), where h and L are the height and lateral distance, respectively, from the center of mass to the pivot point when the animal is upright on a horizontal surface.