Running on water added to gecko's impressive list of capabilities

Research: Geckos combine surface tension with foot slapping to stay above water surface —

Running on water added to gecko's impressive list of capabilities

In fact, they are able to run at almost a meter, or three feet, per second over water and easily transition to speeding across solid ground or climbing up a vertical surface. Meanwhile, larger animals such as the grebe, can walk on water because they are powerful enough to slap the surface with their feet as they run.

But the gecko is of intermediate size: at about 6 grams (one-fifth of an ounce, or the weight of a sheet of paper), they are too large to float above the surface, but too light to keep their bodies above water by slapping forces only. Soap reduces water tension, and sure enough, the geckos sunk farther into the water, forcing them to rely on a swimming action to make it out of the suds.

Dr. Jasmine Nirody from the Oxford University chose to study geckos' "superpower" of walking on water and solve out this scientific "puzzle", once and for all. It's thanks to their rapid slapping that the geckos are still able to run over water - but only briefly because it requires a lot of energy, the authors reported in the journal Current Biology.

Some insects, such as fishing spiders and water striders, habitually walk on the surface of water easily. It is even more interesting because of the fact that surface tension is typically highly important only in much smaller creatures, and has been seen to be unimportant for basilisks, lizards with water-walking abilities as well.

Geckos have this awesome superhydrophobic skin that repels water and enhances their ability to stay above the surface. Some animals, however, have evolved techniques to keep most of their body above the water's surface as they traverse ponds and puddles.

Geckos are some very special reptiles, boasting several fascinating abilities, including walking up walls, gliding through the air, and running on water, all together bringing geckos the nickname of "superheroes of the reptile world". Lighter animals, mostly insects, are supported by surface tension alone.

For all the ingenuity of this multi-tasking approach, geckos can only keep their head and torso fully above the water, leaving their tails dragging underneath. Lab experiments show how.

"When they hit the water they actually create an air bubble, which generates extra force and helps their body stay above the surface", says Nirody.

Prof Full explained: "Bigger animals can't use surface tension, so they end up pushing and slapping the surface, which produces a force if you do it hard enough".

But they also seem to use their smooth, water-repellent skin to plane across the surface, similar to hydroplaning but referred to as semi-planing, a technique used by muskrats.

We also found that geckos crucially use a combination of hydrostatic force (the upwards push of the water known as buoyancy) and hydrodynamic force (the lift created by movement across the water's surface like in a surface-skimming motorboat).

So they built a long water tank and placed flat-tailed house geckos common in south and southeast Asia on a plank.

The geckos were startled by having their tail touched and high-speed video recorded their water walking techniques and estimate the forces involved. "The way that they combine several modalities to perform this feat is really remarkable".

Study co-authors include Judy Jinn, National Science Foundation Graduate Fellow at UC Berkeley; Thomas Libby of UC Berkeley and the University of Washington; Georgia Tech graduate research assistant Timothy Lee and associate professor David Hu; and Max Planck Institute research group leader Ardian Jusufi.

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