Geckos bathe with tiny drops, use their tails as optional legs, and can alter the stickiness of their feet as needed. They come in brilliant colors, and make charismatic mascots. And now we know that they can run on water, Inside Science reports.
Ardian Jusufi, a biophysicist at Germany’s Max Planck Institute for Intelligent Systems, was observing flat-tailed house geckos in a Singapore rainforest when he noticed their ability to evade predators by scampering over puddles. Not through them, he observed, but "on the water’s surface," as Jusufi and his coauthors write in a Current Biology study published yesterday. It was an impressive sight, but it wasn't until they conducted lab experiments that the true extent of the lizards’ aquatic dexterity was revealed.
The researchers found that the geckos could run at the speed of nearly three feet per second. That’s faster than ducks, mink, muskrats, marine iguanas, and juvenile alligators can swim, the researchers write. Predators, in other words, can eat their wakes.
But just how do the geckos do it? They’re not the only species that can walk on water—the basilisk lizard is famous for it, the insects called water striders, too—but the geckos don't do it in quite the same way. They're not heavy enough to create enough force just by slapping the water like the larger lizards, and they're too heavy to sit on water's surface tension like a bug.
Experiments revealed that the geckos combine four distinct techniques. First, they actually do utilize surface tension. When the team added surfactant to the water, the geckos’ velocity was cut in half. Second, the geckos also slap the water with all four legs, which creates air cavities like basilisks do. Third, they benefit from their water-repellent skin. And finally, the geckos undulate their bodies—even their submerged trunks and tails—to propel themselves forward, a little like a butterfly stroke.
There’s more at stake in these findings than geckos’ ability to outrun predators. Coauthor Robert J. Full, of the University of California, Berkeley, tells Inside Science that the geckos may provide a model for robots that could gracefully “run and climb and race across the water” to conduct rescue missions.
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