Geckos Race Across the Water's Surface Using Multiple Mechanisms.

Acrobatic geckos can sprint at high speeds over challenging terrain [1], scamper up the smoothest surfaces [2], rapidly swing underneath leaves [3], and right themselves in midair by swinging only their tails [4, 5]. From our field observations, we can add racing on the water's surface to the gecko's list of agile feats. Locomotion at the air-water interface evolved in over a thousand species, including insects, fish, reptiles, and mammals [6]. To support their weight, some larger-legged vertebrates use forces generated by vigorous slapping of the fluid's surface followed by a stroke of their appendage [7-12], whereas smaller animals, like arthropods, rely on surface tension to walk on water [6, 13]. Intermediate-sized geckos (Hemidactylus platyurus) fall squarely between these two regimes. Here, we report the unique ability of geckos to exceed the speed limits of conventional surface swimming. Several mechanisms likely contribute in this intermediate regime. In contrast to bipedal basilisk lizards [7-10], geckos used a stereotypic trotting gait with all four limbs, creating air cavities during slapping to raise their head and anterior trunk above water. Adding surfactant to the water decreased velocity by half, confirming surface tension's role. The superhydrophobic skin could reduce drag during semi-planing. Geckos laterally undulated their bodies, including their submerged posterior trunk and tail, generating thrust for forward propulsion, much like water dragons [14] and alligators [15]. Geckos again remind us of the advantages of multi-functional morphologies providing the opportunity for multiple mechanisms for motion.