Burrowing dynamics of aquatic worms in soft sediments
Burrowing dynamics of aquatic worms in soft sediments
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DOI：
10.1073/pnas.1911317116
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发表时间：
2019-12-17
影响因子：
11.1
通讯作者：
Ramirez, Bernny
中科院分区：
文献类型：
--
作者：
Kudrolli, Arshad;Ramirez, Bernny
为了了解湖泊和海洋底部发现的底栖动物带中的无肢体运动，我们研究了饱和水层中的变形虫的动态。观察到这些细长的水生蠕虫在饱和水的沉积物和水中都表现出伸缩和横向波动。在沉积物介质中观察到更大的阻力各向异性，与使用阻力辅助推进在水中以相同的行程游泳相比，可以提高蠕虫的挖掘速度。通过结合粘性流体中波动运动的阻力理论和沉积物中蠕动运动的动态锚模型的计算形式，我们捕捉到了观测到的速度。研究发现，蠕动对于在非粘性沉积物中挖洞是有效的，这些沉积物在沉积物床内的移动体后面快速填充。而波动冲程在水和浅沉积层中被发现是有效的，在那里锚定不可能实现蠕动运动。我们发现，这种双重中风也出现在蚯蚓Eisenia Fetida中，这种蚯蚓生活在潮湿的沉积物中，容易发生洪水。我们对介质流变性的分析表明，生物利用双重冲程来协商沉积床，这些沉淀层可能是非均匀填充的，活跃的入侵者可以利用这种双重冲程有效地从流体通过易于流态化的松散床表层移动到下面的固结良好的床。
We investigate the dynamics of Lumbriculus variegatus in water-saturated sediment beds to understand limbless locomotion in the benthic zone found at the bottom of lakes and oceans. These slender aquatic worms are observed to perform elongation-contraction and transverse undulatory strokes in both water-saturated sediments and water. Greater drag anisotropy in the sediment medium is observed to boost the burrowing speed of the worm compared to swimming in water with the same stroke using drag-assisted propulsion. We capture the observed speeds by combining the calculated forms based on resistive-force theory of undulatory motion in viscous fluids and a dynamic anchor model of peristaltic motion in the sediments. Peristalsis is found to be effective for burrowing in noncohesive sediments which fill in rapidly behind the moving body inside the sediment bed. Whereas the undulatory stroke is found to be effective in water and in shallow sediment layers where anchoring is not possible to achieve peristaltic motion. We show that such dual strokes occur as well in the earthworm Eisenia fetida which inhabits moist sediments that are prone to flooding. Our analysis in terms of the rheology of the medium shows that the dual strokes are exploited by organisms to negotiate sediment beds that may be packed heterogeneously and can be used by active intruders to move effectively from a fluid through the loose bed surface layer which fluidizes easily to the well-consolidated bed below.