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Here’s how geckos (almost) walk on water



Add the water aerobics to the list of athletic achievements of the agile gecko.

In addition to sticking to smooth walls and swinging from leaves, geckos can jump on the surface of the water. By crushing the water with all four limbs to create air bubbles and using the surface tension of the water, the reptiles can travel at speeds close to what they can get on the ground, according to a new analysis of the high-speed video described on December 6 in Current Biology .

In the world of water walkers, geckos occupy a strange intermediate terrain, says study co-author Jasmine Nirody, a biophysicist at Rockefeller University in New York and Oxford University. Small insects like striders use surface tension, created by water molecules that stick together, to stay afloat. Larger animals like basilisk lizards slap the surface of the water, creating air pockets around their feet that reduce drag and keep lizards mostly above the surface of the water. But an animal needs to be big enough to generate enough strength to keep out of the water using that strategy.

"Geckos fall face down in the middle," says Nirody. "They should not really be able to do it at all". Yet when his colleague, Ardian Jusufi, of the Max Planck Institute for Intelligent Systems in Stuttgart, Germany, was on vacation in Singapore, he noticed small geckos darting across the surface of puddles.

Back in the laboratory, the team filmed eight flat-tailed house geckos ( Hemidactylus platyurus ) through a pool of water, then slowed down the footage to give a closer look. close to the action. [1

9659002] All four limbs slap the water in a sort of inelegant, extra-splashy front elbow shot, while the wavy tail adds forward propulsion, the researchers found. While the geckos back the legs remain submerged, 70% of their front body is out of the water. Since water is more difficult to cross than air, this positioning helps geckos to cross water at about 10.5 body lengths, or up to almost one meter per second. It's almost as fast as moving on land and much faster than expected if we swim completely submerged.

"The thing that is pretty spectacular about these animals is that they look like they crawled in front of the water," says Tonia Hsieh, a biomechanics researcher at Temple University in Philadelphia who has studied the slap behavior of the lizards of the basilisk.

Despite the rowing with four limbs instead of two like the lizards of the basilisk, the geckos could not generate almost as much strength. It is sufficient to support only about 30 percent of their weight, calculated by Nirody. And when he added dish soap to the water to reduce surface tension, the geckos could not move nearly as fast. This suggests that while surface tension alone can not support geckos like a tiny insect can, it still gives an extra boost. Even the superhydrophobic skin that repels water helps to further reduce the resistance.

Geckos do not really walk on water in the way, for example, that water spiders do, Nirody admits. "They are doing some sort of mixed-mode movement, combining the techniques used for walking and swimming." One day, he hopes, the gecko hybrid approach could help researchers create robots that can travel more efficiently through water.


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