Sharpe Sarah S, Koehler Stephan A, Kuckuk Robyn M, Serrano Miguel, Vela Patricio A, Mendelson Joseph, Goldman Daniel I
Interdisciplinary Bioengineering Program, Georgia Tech, Atlanta, GA 30332-0363, USA Department of Biomedical Engineering, Georgia Tech, Atlanta, GA 30332-0363, USA.
School of Engineering and Applied Sciences, Harvard University, Cambridge, MA 02138, USA.
J Exp Biol. 2015 Feb 1;218(Pt 3):440-50. doi: 10.1242/jeb.108357. Epub 2014 Dec 18.
Squamates classified as 'subarenaceous' possess the ability to move long distances within dry sand; body elongation among sand and soil burrowers has been hypothesized to enhance subsurface performance. Using X-ray imaging, we performed the first kinematic investigation of the subsurface locomotion of the long, slender shovel-nosed snake (Chionactis occipitalis) and compared its biomechanics with those of the shorter, limbed sandfish lizard (Scincus scincus). The sandfish was previously shown to maximize swimming speed and minimize the mechanical cost of transport during burial. Our measurements revealed that the snake also swims through sand by propagating traveling waves down the body, head to tail. Unlike the sandfish, the snake nearly followed its own tracks, thus swimming in an approximate tube of self-fluidized granular media. We measured deviations from tube movement by introducing a parameter, the local slip angle, βs, which measures the angle between the direction of movement of each segment and body orientation. The average βs was smaller for the snake than for the sandfish; granular resistive force theory (RFT) revealed that the curvature utilized by each animal optimized its performance. The snake benefits from its slender body shape (and increased vertebral number), which allows propagation of a higher number of optimal curvature body undulations. The snake's low skin friction also increases performance. The agreement between experiment and RFT combined with the relatively simple properties of the granular 'frictional fluid' make subarenaceous swimming an attractive system to study functional morphology and bauplan evolution.
被归类为“亚沙生”的有鳞目动物具有在干燥沙地中长距离移动的能力；据推测，在沙地和土壤中挖掘洞穴的动物身体伸长有助于提高地下活动能力。我们利用X射线成像技术，首次对细长的铲鼻蛇（Chionactis occipitalis）的地下运动进行了运动学研究，并将其生物力学与较短的有肢沙鱼蜥（Scincus scincus）进行了比较。此前研究表明，沙鱼蜥在埋入沙中时能使游泳速度最大化，并将运输的机械成本降至最低。我们的测量结果显示，蛇也是通过沿着身体从头到尾传播行波在沙中游泳。与沙鱼蜥不同的是，蛇几乎沿着自己的轨迹游动，因此是在由自身流化的颗粒介质构成的近似管道中游泳。我们通过引入一个参数——局部滑移角βs来测量与管道运动的偏差，该参数测量的是每个身体节段的运动方向与身体朝向之间的夹角。蛇的平均βs比沙鱼蜥小；颗粒阻力理论（RFT）表明，每种动物所利用的曲率优化了其性能。蛇得益于其细长的体型（以及增加的椎骨数量），这使得更多数量的最佳曲率身体波动得以传播。蛇的低皮肤摩擦力也提高了其性能。实验与RFT之间的一致性，再加上颗粒“摩擦流体”相对简单的特性，使得亚沙生游泳成为研究功能形态学和bauplan进化的一个有吸引力的系统。
