Speed modulation in swimming frogs

Swimming movements of 7 European green frogs (Rana esculenta) were studied, starting from the detailed analysis of the speed and timing of the propuls ive, glide, and recovery phases of their intermittent swimming behavior. Fi rst, the authors identified the spatiotemporal factors used by the frogs to modulate their swimming behavior. None of the gait variables correlated st rongly with average swimming speed, and no significant correlations were fo und between variables belonging to different phases. There did not seem to be an obvious control strategy. Instantaneous speeds at the transition of t he different phases all increased significantly with average speed, however . The strong correlation between maximal speed at the end of propulsion and the speed averaged over a cycle might reflect the dominance of the propuls ive phase in the determination of the overall swimming speed. The modulatio n of swimming speed thus seemed largely comparable with the regulation of j umping distance. That finding was confirmed in a mathematical model, in whi ch the positive correlations between both glide and recovery speeds, on the one hand, and average speed, on the other, were shown to be only mathemati cal consequences of the strong impact of the propulsive phase on overall sw imming performance. That finding suggests that the correlations did not res ult from an active control strategy.