LOCHETTO, S.M.**; JAYNE, B.C.; Univ. of Cincinnati: Size affects the gap-bridging performance of brown tree snakes

Environmental variation often has profound effects on the locomotion of animals, and networks of branches in arboreal environments provide a rich source of variation in physical structure that imposes several functional challenges. For example, gaps between branches in arboreal environments often must be traversed, and the elongate bodies of snakes theoretically are well suited for this task. However, only one study has previously investigated gap bridging in snakes, and the effects of size are poorly understood. Thus, we videotaped and quantified maximal gap-bridging ability in a highly arboreal species of snake (Boiga irregularis), for which we were able to obtain a large range in snout-vent length (SVL = 43-188 cm) and mass (10-1391 g). We expected that smaller snakes would be able to bridge relatively larger gaps that larger individual because of the proportionately higher ratio of muscle cross-sectional area to mass. The length of the maximal gap spanned (cm) by B. irregularis had the following highly significant relationship with snake length: gap = 9.3 + 0.36SVL (r²=0.88, P<0.001, N=24). Thus, the scaling equation predicts that smaller snakes can span a greater proportion of their length than larger snakes, and the greatest relative gap distance spanned (64% SVL) was in the smallest individual. To span large gaps, the brown tree snakes frequently encircled the posterior perch with their tail. Rather than simply extending straight forward from one perch to another, some snakes (shown in video) inclined the neck as much as forty five degrees and then lunged forward and downward towards the anterior perch. Perhaps the launching behavior of the gliding tree snakes (Chrysopelia) evolved from an ancestral behavior of lunging to bridge gaps similar to that we have observed for the brown tree snakes.