UC Berkeley

Navigation of complex environments is crucial for animals to find food, mates and/or shelter and to escape enemies. In order to move successfully in variable conditions, many animals have evolved the ability to switch between several patterns of locomotion or gaits. Here, we describe and differentiate between putative locomotor gaits in the harvestman, an arachnid that uses a hexapod-like alternate tripod gait. We recorded Neotropical harvestmen of the genus Prionostemma moving across a flat surface using high-speed video. We reconstructed three-dimensional trajectories and associated kinematics and found four different locomotor gaits: running, stotting, bobbing and walking. Gaits differed in their performance and postural kinematics, body trajectory, gait diagrams and/or kinetic and potential energy exchange. Our approach points out the importance of using multiple kinematic features to differentiate gaits. The use of a specific gait was not predicted by leg length, body area or sex. We propose testable hypotheses regarding the function of each gait and the factors that drive the evolution of different gaits. Ultimately, the diversity of locomotory gaits can allow animals to respond to different environmental challenges and contexts.