Locomotion of Skittering Frogs at the Air-water Interface

Many animals interact with the air-water interface during locomotion. Such location either involves moving through the water's surface or moving atop the water surface. This dissertation aims to investigate both of these forms of locomotion in frogs. First we quantified the kinematics of skittering, jumping on top the water's surface without sinking, in two species of frog, Acris crepitans and Euphlyctis cyanophlyctis. We found that what was described as "skittering" locomotion in Acris crepitans is actually more akin to porpoising. A. crepitans begins and ends each jump during their interfacial behavior under the water surface. These frogs may be unable to perform true skittering locomotion due to not being able to retract their hindlimbs fast enough. E. cyanophlyctis, however, does stay above the water surface during this mode of locomotion. We found that Euphlyctis is highly maneuverable during skittering locomotion compared to other inertial based water-surface traversing animals. Not only can they turn up to 80° between subsequent jumps, they also perform this behavior in close proximity to each other without collision. Next, we investigated control mechanisms used by frogs when jumping from water. Prior research has identified frogs of the genus Euphlyctis as high jumpers. But previous studies only considered their maximal performance. Here, we investigated how these frogs modulate propulsive force in order to control their jump height. We linked the frog limb kinematics to the jump force by modeling the added mass produced by the foot's motion.