This ability to modify gripping arc length may allow snakes to increase the grip force they can apply, but increased gripping arc has the potential cost of decreasing the number of grips due to the limited length of the snake and increasing the lateral distance that must be moved.Ĭoncertina locomotion can be an extremely demanding mode of locomotion and hence is well suited for gaining insights into how environmental variation affects organismal performance and musculoskeletal function. Unlike limbed animals, whose grasp on a given diameter perch is limited by finger or arm span, snakes can change the length of their body that encircles the perch. Similar to primates, snakes use a frictional grip, the strength of which depends upon the extent to which the grip encircles the perch( Cartmill, 1974 Cartmill, 1985). However, such a variety of movements will be restricted by the need to fit on branches. The flexible, elongate bodies of snakes may allow them to fit onto and conform easily to different sizes of perches and to use a wide range of postures and movements. The limbless form of snakes provides a conspicuously different body plan in which to examine the effects of various aspects of arboreal habitat structure, with the variation in behavior and kinematics giving insights into the general principles underlying all arboreal locomotion. The arboreal locomotion of snakes is interesting for several reasons. Although many species of snake are arboreal and have convergently evolved anatomical specializations for arboreal life( Jayne, 1982 Lillywhite, 1987 Lillywhite and Henderson,1993), no previous study has determined how any species of snake moves on cylindrical surfaces that typify the branches found in arboreal habitats. Large diameters generally allow faster forward locomotor speed when lizards are moving on top of the perch( Losos and Sinervo, 1989). Within vertebrates, arboreal locomotion is best studied for primates and lizards ( Cartmill, 1974 Losos and Sinervo, 1989), in which the effects on limb kinematics( Higham and Jayne, 2004 Larson and Stern, 2004 Schmitt, 1998 Spezzano and Jayne, 2004) and locomotor performance ( Losos and Irschick,1996 Losos and Sinervo,1989 Sinervo,1991) are well known. The diameter of perches has numerous and important consequences for gripping and fitting onto the perch during locomotion, and progressively steeper inclines increase the influence of the animal's weight parallel to the direction of forward movement. Animals moving in arboreal habitats face numerous functional demands arising from variable surface diameters and inclines and the need to traverse gaps, to grip and balance on cylindrical perches and to fit onto the perch( Cartmill, 1985). However, the slower speeds on horizontal perches compared to tunnels also suggest that balance and grip may further limit locomotor performance.Īrboreal locomotion provides an excellent example of how environment affects behavior and function. The numerous effects of perch diameter on kinematics and the similarity to tunnel concertina locomotion emphasize the importance of fit as a limitation in arboreal locomotion of snakes. When perches and tunnels were narrower, the snakes had more lateral bends at shallower angles. Both tunnel width and perch diameter had widespread and similar effects on kinematics. Mean forward velocity decreased both with increased incline and with increased perch diameter, contrary to the beneficial effect of increased diameter on the speeds of lizards. When moving downhill, snakes often slid continuously while grasping the perch to reduce their speed. On horizontal and uphill perches snakes performed a variant of concertina locomotion with periodic stopping and gripping. None of the locomotion on perches conformed to any previously described mode of limbless locomotion. When perches were inclined at either 45° or 90°, snakes were unable to move uphill or downhill on the larger diameters. We quantified the kinematics and performance of corn snakes ( Elaphe guttata) moving on seven cylinders (diameters 1.6–21 cm) with five inclines (horizontal, ±45° and☙0°) and through horizontal tunnels of corresponding widths. In contrast to lizards and primates, the arboreal locomotion of snakes is poorly understood, despite numerous snake species being arboreal. Animals moving through arboreal habitats face several functional challenges, including fitting onto and moving on cylindrical branches with variable diameters and inclines.
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