Perch diameter and branching patterns have interactive effects on the locomotion and path choice of anole lizards

Abstract

SUMMARYNatural branches vary conspicuously in their diameter, density and orientation, but how these latter two factors affect animal locomotion is poorly understood. Thus, for three species of arboreal anole lizards found on different size branches and with different limb lengths, we tested sprinting performance on cylinders with five diameters (5-100mm) and five patterns of pegs, which simulated different branch orientations and spacing. We also tested whether the lizards preferred surfaces that enhanced their performance. The overall responses to different surfaces were similar among the three species, although the magnitude of the effects differed. All species were faster on cylinders with larger diameter and no pegs along the top. The short-limbed species was the slowest on all surfaces. Much of the variation in performance resulted from variable amounts of pausing among different surfaces and species. Lizards preferred to run along the top of cylinders, but pegs along the top of the narrow cylinders interfered with this. Pegs on top of the 100-mm diameter cylinder, however, had little effect on speed as the lizards ran quite a straight path alongside pegs without bumping into them. All three species usually chose surfaces with greater diameters and fewer pegs, but very large diameters with pegs were preferred to much smaller diameter cylinders without pegs. Our results suggest that preferring larger diameters in natural vegetation has a direct benefit for speed and an added benefit of allowing detouring around branches with little adverse effect on speed. Supplementary material available online at

Why arboreal snakes should not be cylindrical: body shape, incline and surface roughness have interactive effects on locomotion

“…Furthermore, many previous studies have used pegs to control and manipulate the spacing and number of points contacted by snakes to clarify the effects of surface structure on locomotor performance, kinematics and force transmission during the terrestrial and arboreal lateral undulation of snakes (Gray and Lissmann, 1950;Bennet et al, 1974;Kelley et al, 1997;Jayne et al, 2013). However, all of these previous studies of snakes and additional studies of limbed arboreal animals (Hyams et al, 2012;Jones and Jayne, 2012) used pegs taller than the height of the animal.…”

“…For limbed animals, peg-like objects as high as the animal create obstacles that impede running (Hyams et al, 2012;Jones and Jayne, 2012). However, because the limbs of animals elevate their bodies above surfaces, certain heights of irregularities in the surface could be of little consequence.…”

“…However, because the limbs of animals elevate their bodies above surfaces, certain heights of irregularities in the surface could be of little consequence. For arboreal limbed animals, such as anole lizards and mice running parallel to the long axis of a cylinder, decreased cylinder diameter decreases the clearance between the surface and the belly for a given limb posture, but unlike snakes, limbed animals can modulate their limb posture to increase clearance between their belly and the surface (Spezzano and Jayne, 2004;Hyams et al, 2012;Jones and Jayne, 2012). Of the snakes we studied, B. constrictor was the only species that occasionally actively used vertebral flexion to clear pegs as high as 10 mm (during concertina locomotion).…”

“…For example, challenges for moving on branches in arboreal habitats include: (1) balancing on narrow cylindrical surfaces, (2) lifting the weight of the animal up inclines and (3) preventing slipping around the circumference of branches or down inclines (Cartmill, 1985). For a variety of limbed and limbless vertebrates, previous studies have quantified the effects on performance of variation in arboreal habitat structure such as surface diameter, the presence and spacing of secondary branches, and inclines (Irschick and Losos, 1999;Mattingly and Jayne, 2004;Astley and Jayne, 2009;Hyams et al, 2012;Jones and Jayne, 2012;Jayne et al, 2013). The roughness of tree bark also varies considerably among different species and among different branches within a single tree (Ferrenberg and Mitton, 2014), but the effects of surface roughness are poorly understood for the locomotion not only of arboreal animals but also of animals in general.…”

“…For example, pegs (simulating secondary branches) along the top of cylinders impede the running of limbed lizards (Jones and Jayne, 2012), whereas they facilitate generating propulsive forces as arboreal snakes push the sides of their bodies against the pegs and perform lateral undulatory locomotion (Astley and Jayne, 2009;Jayne and Herrmann, 2011). In fact, pegs can allow snakes to traverse large diameter cylinders that would otherwise be impassable (Astley and Jayne, 2009;Jayne and Herrmann, 2011).…”