Department of Physics and Center for Brain Science, Harvard University, Cambridge, MA 02138, USA.
Proc Natl Acad Sci U S A. 2010 Nov 23;107(47):20323-8. doi: 10.1073/pnas.1003016107. Epub 2010 Nov 3.
To navigate different environments, an animal must be able to adapt its locomotory gait to its physical surroundings. The nematode Caenorhabditis elegans, between swimming in water and crawling on surfaces, adapts its locomotory gait to surroundings that impose approximately 10,000-fold differences in mechanical resistance. Here we investigate this feat by studying the undulatory movements of C. elegans in Newtonian fluids spanning nearly five orders of magnitude in viscosity. In these fluids, the worm undulatory gait varies continuously with changes in external load: As load increases, both wavelength and frequency of undulation decrease. We also quantify the internal viscoelastic properties of the worm's body and their role in locomotory dynamics. We incorporate muscle activity, internal load, and external load into a biomechanical model of locomotion and show that (i) muscle power is nearly constant across changes in locomotory gait, and (ii) the onset of gait adaptation occurs as external load becomes comparable to internal load. During the swimming gait, which is evoked by small external loads, muscle power is primarily devoted to bending the worm's elastic body. During the crawling gait, evoked by large external loads, comparable muscle power is used to drive the external load and the elastic body. Our results suggest that C. elegans locomotory gait continuously adapts to external mechanical load in order to maintain propulsive thrust.
为了在不同环境中导航，动物必须能够根据其物理环境调整其运动步态。秀丽隐杆线虫（Caenorhabditis elegans）在水中游泳和在表面爬行之间，会根据其运动所面临的机械阻力相差约 10000 倍的环境来调整其运动步态。在这里，我们通过研究 C. elegans 在牛顿流体中的波动运动来研究这一壮举，这些牛顿流体的粘度跨越了近五个数量级。在这些流体中，蠕虫的波动步态随外部负载的变化而连续变化：随着负载的增加，波动的波长和频率都会降低。我们还量化了蠕虫身体的内部粘弹性特性及其在运动动力学中的作用。我们将肌肉活动、内部负载和外部负载纳入运动的生物力学模型，并表明：(i) 肌肉功率在运动步态变化时几乎保持不变，(ii) 当外部负载与内部负载相当时，运动步态的适应性开始出现。在由小外部负载引发的游泳步态中，肌肉功率主要用于弯曲蠕虫的弹性体。在由大外部负载引发的爬行步态中，相当的肌肉功率用于驱动外部负载和弹性体。我们的研究结果表明，C. elegans 的运动步态会持续适应外部机械负载，以保持推进力。
