JEB desktop wallpaper calendar 2016

JEB desktop wallpaper calendar 2016

Substrate diameter and compliance affect the gripping strategies and locomotor mode of climbing boa constrictors
Greg Byrnes, Bruce C. Jayne

SUMMARY

Arboreal habitats pose unique challenges for locomotion as a result of their narrow cylindrical surfaces and discontinuities between branches. Decreased diameter of branches increases compliance, which can pose additional challenges, including effects on stability and energy damping. However, the combined effects of substrate diameter and compliance are poorly understood for any animal. We quantified performance, kinematics and substrate deformation while boa constrictors (Boa constrictor) climbed vertical ropes with three diameters (3, 6 and 9 mm) and four tensions (0.5, 1.0, 1.5 and 2.0 body weights). Mean forward velocity decreased significantly with both decreased diameter and increased compliance. Both diameter and compliance had numerous effects on locomotor kinematics, but diameter had larger and more pervasive effects than compliance. Locomotion on the largest diameter had a larger forward excursion per cycle, and the locomotor mode and gripping strategy differed from that on the smaller diameters. On larger diameters, snakes primarily applied opposing forces at the same location on the rope to grip. By contrast, on smaller diameters forces were applied in opposite directions at different locations along the rope, resulting in increased rope deformation. Although energy is likely to be lost during deformation, snakes might use increased surface deformation as a strategy to enhance their ability to grip.

FOOTNOTES

  • LIST OF SYMBOLS AND ABBREVIATIONS

    Freq
    normal force required to attain observed ΔTmax
    lmax
    maximum longitudinal extension of body and tail along the rope
    lmin
    minimum longitudinal extension of body and tail along the rope
    Ncr.max
    number of crossing regions at lmax
    Ncr.min
    number of crossing regions at lmin
    rc
    radius of curvature
    tcycle
    cycle duration in seconds
    vx
    average velocity of a cycle
    αcr
    mean angle of the body midline with respect to the long axis of the rope at crossing regions during maximal static contact
    ΔNcr
    change in number of crossing regions
    ΔTmax
    maximum change in tension due to deformation within a cycle
    Δx
    distance traveled per cycle
    μs
    coefficient of static friction
    %stat
    percentage of a cycle in static contact with the substrate

  • This work was supported by NSF grant IOS 0843197 to B.C.J. We thank H. Ofori-Sampong for her assistance throughout the project. We also thank two anonymous reviewers for their comments that have improved the manuscript.

  • Supplementary material available online at http://jeb.biologists.org/cgi/content/full/213/24/4249/DC1

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