Biophysics Graduate Group, University of California, Berkeley, Stanley Hall, Berkeley, CA 94720, USA; All Souls College, University of Oxford, High Street, Oxford OX14AL, UK; Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX13PU, UK; Center for Studies in Physics and Biology, The Rockefeller University, 1302 York Ave., New York, NY 10065, USA.
Department of Psychology, University of California, Berkeley, 2121 Berkeley Way, Berkeley, CA 94720, USA.
Curr Biol. 2018 Dec 17;28(24):4046-4051.e2. doi: 10.1016/j.cub.2018.10.064. Epub 2018 Dec 6.
Acrobatic geckos can sprint at high speeds over challenging terrain [1], scamper up the smoothest surfaces [2], rapidly swing underneath leaves [3], and right themselves in midair by swinging only their tails [4, 5]. From our field observations, we can add racing on the water's surface to the gecko's list of agile feats. Locomotion at the air-water interface evolved in over a thousand species, including insects, fish, reptiles, and mammals [6]. To support their weight, some larger-legged vertebrates use forces generated by vigorous slapping of the fluid's surface followed by a stroke of their appendage [7-12], whereas smaller animals, like arthropods, rely on surface tension to walk on water [6, 13]. Intermediate-sized geckos (Hemidactylus platyurus) fall squarely between these two regimes. Here, we report the unique ability of geckos to exceed the speed limits of conventional surface swimming. Several mechanisms likely contribute in this intermediate regime. In contrast to bipedal basilisk lizards [7-10], geckos used a stereotypic trotting gait with all four limbs, creating air cavities during slapping to raise their head and anterior trunk above water. Adding surfactant to the water decreased velocity by half, confirming surface tension's role. The superhydrophobic skin could reduce drag during semi-planing. Geckos laterally undulated their bodies, including their submerged posterior trunk and tail, generating thrust for forward propulsion, much like water dragons [14] and alligators [15]. Geckos again remind us of the advantages of multi-functional morphologies providing the opportunity for multiple mechanisms for motion.
会杂技的壁虎能在崎岖不平的地形上高速冲刺[1]，能在最光滑的表面上飞奔[2]，能在树叶下迅速摆动[3]，还能只用尾巴在空中翻转[4,5]。从我们的实地观察来看，我们可以在壁虎的敏捷壮举列表中再加上在水面上奔跑。在包括昆虫、鱼类、爬行动物和哺乳动物在内的一千多种物种中，空气-水界面的运动已经进化[6]。为了支撑它们的体重，一些腿部较大的脊椎动物利用拍打流体表面产生的力量，然后再用它们的附肢划一下[7-12]，而像节肢动物这样的较小动物，则依靠表面张力在水面上行走[6,13]。中等大小的壁虎（扁尾蜥虎）正好处于这两种状态之间。在这里，我们报告了壁虎超越传统水面游泳速度限制的独特能力。在这个中间状态下，可能有几种机制在起作用。与两足蜥蜴（basilisk lizards）不同[7-10]，壁虎使用四足进行典型的小跑步态，在拍打时产生空气腔，将头部和前躯干抬出水面。向水中添加表面活性剂会将速度降低一半，这证实了表面张力的作用。超疏水皮肤可以减少半滑行时的阻力。壁虎的身体会侧向波动，包括其水下的后躯干和尾巴，产生向前推进的推力，就像水龙和短吻鳄一样[14,15]。壁虎再次提醒我们，多功能形态的优势为运动提供了多种机制的机会。
