The new superpower of Geckos is running on water. Now we know how they do it


Geckos are known to be experienced climbers who can stick to any surface thanks to nearly 500,000[[[[corrected]tiny hair-like structures on the feet. Now it turns out that the small lizards can also run at high speed on the water surface to escape predators. You can not do it very long; The energy consumption is too big. But it's amazing that they even make it. Scientists believe that they have pinpointed the mechanisms behind the feat Cell Biology,

The project began when co-author Ardian Jusufi, then a postdoctoral fellow in the University of California's laboratory, Berkeley biophysicist Robert Fullle, was on vacation in Singapore during the monsoon season. One day, after a big rainstorm, he caught a gecko whizzing across the water to escape a predator on video. The material stunned everyone in the lab when he showed it to them. "It was incredibly strange and unexpected, so we had to test that, of course," says fellow co-author Jasmine Nirody, another former student who now lives between Rockefeller University and the University of Oxford.

In nature, there are several creatures that can run on water, but use different mechanisms depending on their size. Small, light runners, for example, rely entirely on surface tension to stay afloat, while the larger, heavier basilisk lizards make a flapping motion with their feet that creates pockets of air bubbles so they do not sink. The theoretical standard calculations set very narrow limits on how small an animal must be to use the surface tension and how big it must be before the surface impact mechanism can work.

The unique gecko passage on the water, as captured by the camera. "Src =" "width =" 640 "height =" 423 "srcset =" https: //cdn.arstechnica .net / wp-content / uploads / 2018/12 / gecko1.jpg 2x
Enlarge / The unique gecko walk on the water as seen on the camera.

Pauline Jennings

Geckos fall somewhere in between. They are too big to rely only on surface tension and too small to generate sufficient force to travel along the water surface without sinking. And yet they can still perform the trick lightning fast – almost one meter per second. Therefore, Full's team decided to investigate further.

They used laser cutters to make entry and exit holes in a large plastic box to make a water tank, and then built two wooden ramps so that their group of Asian geckos (Hemidactylus platyurus) could easily enter and exit the water. A pair of high-speed cameras were placed at the top and sides at right angles to capture the movement. The geckos would be placed on the entrance ramp and the team members would easily touch their tails to make them swim.

Geckos have developed a number of complicated mechanisms to run on water.

It has been found that geckos have developed a number of complicated mechanisms to run on water. Crossing water has two purposes: keeping the body above the surface and keeping the propulsion forward. On the one hand, the gecko combines surface impact and surface tension, supported by its unique hydrophobic skin that repels water, Nirody said. A drop of water just sits on the skin of a gecko.

Lifting your body over the water reduces air resistance, making it easier for geckos to move forward than if completely submerged. They also move with their bodies and tails, similar to swimming. "Looking at them from above, it almost looks like they are just going to swim very fast," says Nirody. "And then you look at her from the side and notice that her upper body and her legs are completely out of the water, though they still perform the swimming motion that drives them forward."

To verify that surface tension actually played a role in the gecko's surface skimming ability, the researchers added a surfactant (rinse aid) to the water. The surface tension occurs because water molecules tend to adhere to each other (molecular adhesion), forming a kind of carrier film that holds very light living beings on the water. When adding soap, the molecules lose this stickiness. Put a watercooler in soapy water and it sinks as it relies completely on surface tension. However, a basilisk lizard is not affected because it relies solely on beating the surface.

Again, the geckos fall somewhere in between. They did not sink, but Nirody et al, The addition of soap to water reduced the speed of geckos by half, most likely because their bodies were much lower in water due to lower surface tension. "We knew that they could not hold all their body weight through the theoretical calculations," Nirody said. This test proved it.

The geckos showed some interesting reactions to the soapy water. About half would double their efforts to swim as fast as possible, although their speed was severely limited. The other half just gave up after the first few strokes and flopped to the floor. Geckos can hold their breath for several minutes, so they were not in immediate danger, even though the team members rescued them after about 30 seconds. "We hypothesized that if they can not shoot in time, instead of slowly getting away from a predator, it's best they just hide underwater and hold their breath," says Nirody.

One goal of this research is to improve the design of robots with biological inspiration. The authors point out that modeling a robot on the lizard of basil would work, but it would require a lot of energy and some kind of active stabilization to make it truly functional. A wavy tail resembling geckos could help with the latter and enhance propulsion while the robot is coated with a hydrophobic material resembling the skin structure of the gecko and could significantly reduce drag. "Nature has so much to teach us," says Nirody. "All these amazing machines are built from which they can see and learn."

Courtesy of the University of Oxford.

DOI: Current biology2018. 10.1016 / j.cub.2018.10.064 (via DOIs).