By Chelsea Whyte
Flat-tailed house geckos can skitter across the surface of water – and now we know how they do it. They keep their upper body in the air by slapping hard on the water and creating pockets of air that help them stay afloat. Though they can swim, running across water is a useful way for them to escape quickly when they are threatened.
Jasmine Nirody at The Rockefeller University in New York and her team investigated how geckos cross water after her colleague visited Singapore during monsoon season and saw the behaviour in the wild.
“To us this was really shocking because when you think about the things that walk on water, you think of these really small insects that can walk using surface tension. Or large bipedal basilisk lizards that generate so much force on the water that they can support their body weight,” she says. “These guys lie smack dab in the middle.”
They took high-speed video of 8 geckos doing 63 runs across a 35-centimetre-long basin filled with water. They found that geckos keep their heads 13.4 millimetres above the surface, on average, while their tails remain in contact with the water. The geckos whirl their front legs in a circle – a little like the way a cartoon character might run. Part of this circle passes through the air and part of it under the water, which helps creates an air pocket that holds the gecko up. They then cycle their back legs to produce forward motion.
“They are partially hydroplaning,” Nirody says. The team also found that geckos can lift up to 72 per cent of their body length out of the water, and that they have superhydrophobic skin that repels water. Both of these factors help reduce drag.
To test whether surface tension has any effect on the geckos ability to run across water, the team added dish soap to the water-filled basin. The soap reduced surface tension by 50 per cent. The geckos could still run across the water, but they travelled at half the speed – which suggests they do exploit surface tension to cross water.
Nirody says previous research shows that basilisk lizards that run across water are unhindered by lower surface tension. The geckos are different: they cross ponds by relying on both the bubbles created by slapping the water and the surface tension of water.
Journal reference: Current Biology, DOI: 10.1016/j.cub.2018.10.064
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