The Strike of a Snake and Body Size

Body size in animals plays a major role in the animal's biology. John Tyler Bonner wrote that "...size is an aspect of the living that plays a remarkable overreaching role that affects life's matter in all its aspects." In a recent paper Herrell et al (2010) investigate size-related changes in defensive strike performance in the White-lipped Green Pit Viper, Trimeresurus (Crypteletrops) albolabris. T. albolabris is an arboreal pit viper from Southeast Asia this is an ambush specialist. However, in some species juveniles select higher, more open foraging sites, possibly giving them a thermal foraging advantage.Thus juvenile arboreal pit vipers may be more exposed while foraging, and consequently subjected to a larger number of predators. Larger individuals tend to forage more in terrestrial situations and usually eat larger prey. The sexes may also be expected to differ in strike performance capacity if they select different prey types, use different types of habitats, or are simply different in size. Striking fast and far is likely of importance in both (defensive and feeding. Fast, long strikes can deter potential predators as well as allow snakes to capture elusive prey.  The authors used 18 female and 17 male albolabris, housed at the Faculty of Science, University of Zagreb, Croatia. They used a digital high speed  camera set at 400 frames per second and filmed 129 strikes made by 29 individual snakes and examined  how defensive strike performance changes with body size in both male and female. Their data show a significant negative allometry in the scaling of head dimensions and head mass to body mass. However, strike velocity and strike distance are independent of body mass, with juveniles in the sample striking as fast and as far as adults. Contrary to model predictions suggesting that acceleration capacity should decrease with increasing body mass, acceleration capacity increases with snake body mass, and that this is the result of a negative allometric scaling of head mass combined with an isometric scaling of the dorsal epaxial musculature. Finally, the data showed a significant sexual dimorphism in body size and strike velocity with females being heavier and striking faster, independent of the dimorphism in body size. Mean strike velocity was 1.5–1.6ms for males and females, respectively.

Literature
Bonner, J. T., 2006. Why Size Matters. Princeton University Press. 161 pp.

Herrel, A., K. Huyghe, P. Okovic´, D. Lisicˇic´, Z. Tadic. 2010. Fast and furious: effects of body size on strike performance in an arboreal viper Trimeresurus (Cryptelytrops) albolabris. Journal of Experimental Zoology. 313A. DOI: 10.1002/jez.645

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