Aquatic and terrestrial locomotor speeds of amphibious sea‐snakes (Serpentes, Laticaudidae)

Abstract

Amphibious animals may be subject to strong but conflicting selective pressures to enhance locomotor performance both on land and in the water. Biomechanical models suggest that in snakes, adaptations to swimming (e.g. reduction of ventral plates, flattening of tail) will reduce their ability to move on land. The locomotor speeds of six taxa of amphibious (laticaudid) sea‐snakes, plus one entirely marine (hydrophiid) species were measured. Because the relative dependence on aquatic vs terrestrial habitats varies with a laticaudid's species, sex and body size, a previous study predicted that these factors should generate significant variation in locomotor speeds within laticaudids. Measurements of swimming and crawling speeds supported this prediction. Some species were faster than others and, within each species, males were faster than conspecific females. The degree of locomotor superiority of males was greater for terrestrial (>40%) than for aquatic (20%) locomotion. Smaller snakes were faster than larger animals in relative speed (body lengths/s) but slower in absolute terms (m/s). The hydrophiid Emydocephalus annulatus was slow in water as well as on land, perhaps because it eats immobile prey and thus, does not depend on speed for foraging. The diversity of locomotor abilities within laticaudid sea‐snakes provides a remarkable opportunity to identify factors that influence evolutionary trade‐offs between conflicting evolutionary optima.

Locomotor behavior across an environmental transition in the ropefish,Erpetoichthys calabaricus

“…Despite the tractability and simplicity of elongate fish as a model system in which to address this question, few studies have directly compared axial-only locomotion in aquatic versus terrestrial environments. In addition, most such studies have considered only undulation frequency and/or overall animal velocity (Jayne, 1986;Shine and Shetty, 2001;Shine et al, 2003), with a much smaller subset encompassing other kinematic variables (Gillis, 1998;Ellerby et al, 2001). …”

Swimming and jumping in a semi-aquatic frog

“…In such cases, natural selection will result in some compromise, i.e., an intermediate phenotype that can perform both tasks reasonably, but never as optimally as a specialised phenotype. Because such trade-offs may be widespread, information on phenotypic traits under such conflicting selective forces may provide general insights into the nature of adaptive compromises (Shine et al, 2003).…”

Locomotor performance of three sympatric species of sea kraits (Laticauda spp.) from Orchid Island, Taiwan

“…In snakes, including sea kraits and other sea snake species, swimming speed increases with an increasing size of individuals (Jayne 1985, Shine and Shetty 2001, Shine et al 2003. Studies of common garter snakes also revealed that a higher maximum crawling speed is associated with an increasing body mass (Heckrotte 1967).…”

“…But Shine et al (2003) also proposed that too little is known about the relative significance of the two types of measures in laticaudine locomotion. Thus, we included both measures of speed in this study.…”

“…The evolutionary transition from terrestrial to aquatic habitats caused subsequent modifications in morphology, physiology, and behavior, especially when strong selective pressures are exerted by aquatic habitats. For example, aquatic snakes that move forward by accelerating portions of the surrounding water (Shine et al 2003) have a laterally compressed body form, a shorter tail, a higher tail height, and a larger tail area (Brischoux and Shine 2011) compared to terrestrial snakes. These character states presumably increase the lateral surface area devoted to thrust and thereby enhance a snake's swimming performance (Pattishall and Cundall 2008).…”