沿浓度细丝冲浪：生理剪切流中精子的趋化性
Surfing along concentration filaments: sperm chemotaxis in physiological shear flows
摘要：
许多能动的生物细胞沿着信号分子的浓度梯度导航：这种趋化性引导例如来自海洋无脊椎动物的精子细胞，它们必须在海洋中找到卵细胞。虽然已经针对静水中旋转对称梯度的理想化条件深入研究了趋化性，但自然梯度通常是扭曲的，例如，海洋中的湍流。最近的实验和直接数值模拟与精子细胞和细菌令人惊讶地表明存在一个最佳的流动强度，在该趋化性是更有效的比静水。我们使用精子趋化性在简单的剪切流作为一个原型的例子来理解这样一个最佳的流动强度的起源理论：我们量化流动如何加速传播的信号分子释放的鸡蛋，但扭曲的浓度场成细长的细丝。这两种效应之间的竞争设定了最佳流动强度，使精卵相遇最大化。我们的特点是如何精子细胞“冲浪”沿浓度细丝，典型的标量湍流，揭示了一个一般的导航模式中存在的流量。我们比较模拟和理论与以前的实验结果，发现很好的协议。
英文摘要：
Many motile biological cells navigate along concentration gradients of signaling molecules: This chemotaxis guides for instance sperm cells from marine invertebrates, which have to find egg cells in the ocean. While chemotaxis has been intensively studied for idealized conditions of rotationally symmetric gradients in still water, natural gradients are usually distorted, e.g., by turbulent flows in the ocean. Recent experiments and direct numerical simulations with sperm cells and bacteria surprisingly suggest the existence of an optimal flow strength at which chemotaxis is more effective than for still water. We use sperm chemotaxis in simple shear flow as a prototypical example to understand the origin of such an optimal flow strength theoretically: We quantify how flow accelerates spreading of signaling molecules released by the egg, but distorts the resulting concentration field into long and thin filaments. The competition between these two effects sets an optimal flow strength that maximizes sperm-egg encounter. We characterize how sperm cells `surf' along concentration filaments, typical for scalar turbulence, revealing a general navigation paradigm in the presence of flow. We compare both simulation and theory with previous experimental results and find good agreement.
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