Arboreal habitats create diverse challenges for animal locomotion, but the numerical and phylogenetic diversity of snakes that climb trees suggest that their overall body plan is well suited for this task. Snakes have considerable diversity of axial anatomy, but the functional consequences of this diversity for arboreal locomotion are poorly understood because of the lack of comparative data. We simulated diverse arboreal surfaces to test whether environmental structure had different effects on the locomotion of snakes belonging to two distantly related species with differences in axial musculature and stoutness. On most cylindrical surfaces lacking pegs, both species used concertina locomotion, which always involved periodic stopping and gripping but was kinematically distinct in the two species. On horizontal cylinders that were a small fraction of body diameter, the boa constrictors used a balancing form of lateral undulation that was not observed for rat snakes. For all snakes the presence of pegs elicited lateral undulation and enhanced speed. For both species maximal speeds decreased with increased incline and were greatest on cylinders with intermediate diameters that approximated the diameter of the snakes. The frictional resistances that we studied had small effects compared with those of cylinder diameter, incline and the presence of pegs. The stouter and more muscular boa constrictors were usually faster than the rat snakes when using the gripping gait, whereas rat snakes were faster when using lateral undulation on the surfaces with pegs. Thus, variation in environmental structure had several highly significant effects on locomotor mode, performance and kinematics that were species dependent.
↵† Present address: Department of Biology, University of Vermont, Burlington, VT 05405, USA
Supplementary material available online at http://jeb.biologists.org/lookup/suppl/doi:10.1242/jeb.055293/-/DC1
This work was supported by NSF grant IOS 0843197 to B.C.J.
LIST OF SYMBOLS AND ABBREVIATIONS
- percentage of a cycle in static contact with the substrate
- minimum length of snake from its snout to tail tip along the x-axis
- number of crossing regions at lmin
- cycle duration in seconds
- average velocity for the fastest cycle or 10 cm
- angle of the body midline with respect to the x-axis from the dorsal view
- forward distance traveled per cycle
- © 2011.