火蚁筏中的集体碾磨允许持续的突起生长
Collective treadmilling in fire ant rafts permits sustained protrusion growth
摘要：
凝聚的活性物质因其变形能力和表现出内部流动而具有示范性，尽管保持凝聚。为了便于理解这种能力，我们调查的原因，手指状突起出现的超级有机体，聚集筏火蚁（红火蚁）。虽然这些特征很容易观察到，但是什么使它们的开始、增长和衰退反复出现，目前还不清楚。蚁筏是由一个漂浮的，相互连接的蚂蚁结构网络组成的，上面有一层自由活动的蚂蚁。在这里，我们表明，持续的形状演变是允许由永久筏收缩之间的竞争，由于散装结构蚂蚁到活动层的位移，和向外筏膨胀由于沉积到结构网络的边缘处的自由蚂蚁之间的竞争所定义的milling。此外，我们看到，突起出现由于表面蚂蚁的边缘沉积速率的不对称性，我们提供了强有力的证据表明，这些不对称性随机发生，由于壁积累效应和局部对齐相互作用。这些效应一起允许合作，但自发形成的突起，火蚁用于功能探索和逃离淹没的环境。蚁筏动力学反映了促进细胞骨架的形态发生和运动性的微铣削，从而提供了另一个例子，其中凝聚的活性物质的重塑被解释为自由成分运输，但其持续依赖于结构和自由成员之间的永久相变。
英文摘要：
Condensed active matter is exemplary for its capacity to morph and exhibit internal flows despite remaining cohered. To facilitate understanding of this ability, we investigate the cause of finger-like protrusions that emerge from super-organismal, aggregated rafts of fire ants (Solenopsis invicta). While these features are easily observed, what permits their recuring initiation, growth, and recession is not immediately clear. Ants rafts are comprised of a floating, structural network of interconnected ants on which a layer of freely active ants walks. We show here that sustained shape evolution is permitted by treadmilling defined by the competition between perpetual raft contraction due to displacement of bulk structural ants into the active layer, and outwards raft expansion due to deposition of free ants into the structural network at the edges. Furthermore, we see that protrusions emerge due to asymmetries in the edge deposition rate of surface ants, and we provide strong evidence that these asymmetries occur stochastically due to wall accumulation effects and local alignment interactions. Together these effects permit the cooperative, yet spontaneous formation of protrusions that fire ants utilize for functional exploration and to escape flooded environments. Ant raft dynamics mirror the treadmilling that facilitates morphogenesis and motility of cytoskeletons, thus providing another example in which reshaping of condensed active matter is explained by free constituent transport, yet whose continuance relies on perpetual phase transition between structural and free members.
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