Do all frogs swim alike? The effect of ecological specialization on swimming kinematics in frogs

Abstract

Abstract Frog locomotion has attracted wide scientific interest due to the unusual and derived morphology of the frog pelvic girdle and hind limb. Previous authors have suggested that the design of the frog locomotor system evolved towards a specialized jumping morphology early-on in the radiation of the group. However, data on locomotion in frogs are biased towards a few groups and most of the ecological and functional diversity remains unexplored. Here we examine the kinematics of swimming in eight species of frog with different ecologies. We use cineradiography to quantify movements of skeletal elements from the entire appendicular skeleton. Our results show that species with different ecologies do differ in the kinematics of swimming with the speed of limb extension and especially the kinematics of the mid-foot being different. Our results moreover suggest that this is not a phylogenetic effect as species from different clades with similar ecologies converge on the same swimming kinematics. These results suggest that it is important to analyze frog locomotion in a broader ecological and evolutionary context if one is to understand the evolutionary origins of this behavior.