Parker Thomas

Abstract:

Locomotion in animals is influenced by the properties of the substrates that they interact with. In arboreal habitats, animals must move over substrates that vary in both orientation and compliance by modulating locomotor forces, maintaining balance, and gripping substrates effectively. These challenges could be even greater in leaping or jumping animals that move by producing large magnitude but transient forces on the substrate during take-off and landing. We explore the interactive effects of substrate orientation and compliance on the jumping performance of tree frogs (Polypedates leucomystax). Frogs were observed jumping from both horizontal and vertical substrates of two different stiffnesses. High-speed video analysis was used to capture takeoff angles and the trajectory of the jumps. Along with video analysis, substrate reaction forces were measured during take-off. In general, frogs reduce the take-off angle relative to the substrate on compliant surfaces, compared to rigid ones, minimizing energy loss to the substrate. However, on vertical compared to horizontal substrates, they jump at greater angles from the substrate for both stiffnesses. In addition, frogs appear to modulate substrate reaction forces less in response to substrate orientation or compliance than take-off angles. Our data give further evidence that branch compliance exerts a cost on locomotion that animals try to minimize, but the frogs in this study appear to balance locomotor costs with maximizing jumping performance.