Meeting Abstract

112.4  Tuesday, Jan. 7 11:00  A kinematic analysis of water-surface locomotion in cricket frogs WEISS, T.M.*; VLACHOS, P.P.; JUNG, S.; SOCHA, J.J.; Virginia Tech; Purdue University; Virginia Tech; Virginia Tech talcat@vt.edu

Multiple species of frogs in the Ranidae family have been observed to ‘skitter’ across the water surface to escape, but little is understood about the biomechanical or physical mechanisms that underlie this behavior. Reports of this unique interfacial locomotion have been documented in literature since the 1950’s, but the best description of this behavior is anecdotal, asserting simply that the frogs can cross the water surface without sinking. The force that propels these frogs several body lengths in the air may originate from the thrust of feet slapping on the water surface, as with basilisk lizards running on water, or it may arise from drag of the webbed feet in the water. To improve our understanding of the biomechanics of this interfacial locomotion, we recorded high speed video of two species of cricket frog (Acris crepitans and Acris gryllus) skittering across the water surface using a glass enclosure and two Photron APX-RS cameras. Contrary to expectations based on anecdotal knowledge of the Indian skipper frog Euphlyctis cyanophlyctis, we found that cricket frogs do not maintain an above-surface orientation throughout the locomotor cycle. Instead, the frogs are almost completely submerged during both the launching and landing phase of a jump cycle. Preliminary analyses of hindlimb extension show that the launch time is very short, ~32 ms (n=13 jumps). Consequently, the thrust required to propel the frog to a height of 1.5 – 2.0 body lengths is generated entirely underwater during a relatively small time frame. These underwater kinematics suggest that the frog propels itself using the drag produced by stroking the feet, a mechanism that differs from the impulse-slap force employed by the basilisk lizard. Supported by NSF PoLS #1205642.