The Modulation of Feeding Behavior in Response to Prey Type in the Frog Rana Pipiens

Using high-speed video motion analysis, the kinematics of feeding behavior was studied in Rana pipiens. Rana pipiens exhibits differing behavior patterns depending upon prey type. When feeding on small prey such as waxworms, R. pipiens uses tongue protraction to catch prey, minimizing head and body movements. When feeding on the larger earthworm, it arches its body, flexes the head downwards and uses jaw prehension to capture the prey. Time to completion of tongue retraction, time to completion of mouth closing, duration of tongue retraction, duration of mouth closing, total time that the mouth is open and maximum tongue reach were significantly longer during waxworm feedings than during earthworm feedings. The tongue angle and degree of head flexion were significantly greater during earthworm feedings. These different kinematic patterns correspond to differences in feeding behavior among major taxa of anurans. Phylogenetically primitive archaeobatrachian frogs have short tongues which can be protracted only a few millimeters. In contrast, many neobatrachians have long tongues which they project to catch small prey. The similarity between the behavior that neobatrachians use to catch large prey and the movement patterns of archaeobatrachians suggests that Rana pipiens has retained the plesiomorphic archaeobatrachian motor pattern and uses it to catch large prey, while evolving a new motor pattern for catching small prey.