Trade-offs between eating and moving: what happens to the locomotion of slender arboreal snakes when they eat big prey?

Abstract

The capacity to consume large prey evolved long ago in snakes. Subsequently, many specialized arboreal snake species convergently evolved slender bodies, presumably well-suited for moving on thin branches and steep slopes, although how this accentuates changes in their shape and weight after eating and creates trade-offs with locomotor performance is poorly understood. Hence, we tested whether the performance and modes of locomotion of a specialized arboreal snake (Boiga irregularis) changed after eating one or two mice when crawling on cylinders with and without pegs and on horizontal or 45° slopes. On surfaces with pegs: (1) only lateral undulation was used; (2) speed decreased with increased meal size; and (3) unexpectedly, more sideways toppling occurred than without pegs. On the horizontal cylinders without pegs, most unfed snakes used lateral undulation with continuous sliding contact, whereas, after eating two mice, most snakes periodically stopped and gripped the cylinder with speeds of concertina locomotion similar to those for the lateral undulation of unfed snakes. Thus, the behaviour of switching to a gripping mode of locomotion (concertina) circumvented some of the constraints of a slender limbless body plan, for which bulky meals alter shape and can impede the movement of the propulsive structures. © 2014 The Linnean Society of London, Biological Journal of the Linnean Society, 2015, 114, 446–458.