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  • Amazing acrobatic geckos

    wall runner

    High speed pictures of Cosymbotus platyurus running up a vertical surface

    I don’t know why, but for some reason herp news stories always seem to come in twos.

    Announced today (or yesterday by the time I get this posted), scientists at UC Berkeley have found geckos to be one of the most agile climbing animals ever studied.

    Jusufi, A., Goldman, D.I., Revzen, S. and Full, R.J. 2008. Active tails enhance arboreal acrobatics in geckos. PNAS. Vol. 105: 4215-4219.

    Goldman et al studied geckos of the species Cosymbotus platyurus. Lizards were ran on vertical surfaces that had various degrees of traction. To induce slippage, some of the surfaces were equipped with a section of dry erase board which had been covered with dry erase ink.

    Apparently geckos can’t grab onto everything after all.

    By placing the lizards at various sections of these surfaces, the researchers were able to get them to either slightly slip, almost fall, or completely.

    The results were interesting.

    For starters, lizards ran up the surfaces with their tails off the “ground” the entire time. That is, unless they slipped. Immediately upon slipping, the tail would come down and act as a brace to keep the body from tilting back and falling off. The most dramatic case of this came from an experiment in which the researchers had dropped the lizards down straight on the dry erase board. The gecko in question fell backward, caught itself with its hindlegs, and tail. The body fell away from the wall about 60? before the tail fully caught the animal, and it was able to right itself again (see photo above).
    self righting gecko
    By far the neatest test performed involved getting the lizards and placing them in a supine (belly up) position on a light polyethylene foil held together with four fishing lines. Then by gently shaking the platform (or waiting for the lizards to slip), they were able to dislodge the geckos and send them plummeting to their doom.

    Doom, in this case, being an embellishment for safely padded landing area.

    The lizards fell 2 meters down. High speed cameras recorded the first 23cm of that trip. These little guys were able to go from fully upside down to rightside up in only 106 milliseconds.

    Let me make sure I’m getting the full effect of that result across:

    These geckos were able to reorient themselves in 106 THOUSANDTHS of a second, or .00106 seconds!!

    Geckos now hold the record for fasting righting time of a vertebrate without the aid of wings.

    This unique feat is accomplished by rotating the substantial tail on these animals. As they fall, the tail is rotated counterclockwise. Physics does the rest. Conservation of angular momentum takes over and the entire body winds up turning clockwise, thus reorienting the animal. This phenomenon is known as: air righting with zero angular momentum. It’s the same effect that cats are often lauded for.

    Cats, and other air righting mammals (e.g. rats) accomplish their air righting maneuvers by flexing and twisting their backs. Evolution removed the need/use for a large powerful tail in mammals, hundreds of millions of years ago.

    No so with lizards. Thanks to this “fifth appendage” all the geckos needed to do was use their tail like a little propeller. There is, however, a caveat.

    Cosymbotus platyurus, like most geckos, is capable of caudal autotomy (i.e. voluntary tail loss). Would lizards that have lost their tails still be able to right themselves?

    Jusufi et al tested this scenario too. They carefully elicited the loss of the tails in some of their experimental animals, and then subjected them to the same tests as before. The results were striking. Tailless lizards were unable to keep themselves from falling in the vertical slip tests. When they were dropped supine, they still righted themselves, but the rate at which they did it was much slower. Tailless geckos relied on the kind of back flexion and twisting seen in mammals.

    Taking things one step further, the authours decided to see how much of a role the tail plays during free fall. They placed the lizards in vertically oriented wind tunnels and “set them free.” The results were unequivocal; the tail acts as the main rudder in these guys. Geckos would rotate their tails counterclockwise to turn left, and clockwise to turn right, while the body remained a stationary airfoil.

    The overall results demonstrated the incredible importance of tails in geckos. This is interesting given that so many geckos are also willing to part with their tails when in danger.

    It seems that in the natural world it’s better to risk knocking oneself out from a fall, than to risk getting eaten by a bodypart that stubbornly stays on.
    It’s unfortunate that the researchers didn’t test the air-righting ability of these geckos after their tails had grown back. Judging from the videos it appears that all the work is being generated by the proximal tail muscles; which stay even after autotomy. Theoretically then, it should still work in a regrown tail.

    Oh yeah, did I forget to mention, Jusufi et al not only recorded everything, but they made them available for everyone to watch.

    They’re all worth watching. It’s cool to see just how fast these little geckos are.

    And so the “slow, sluggish reptile” stereotype, receives yet another nail in its coffin.