Data associated with Matveev et al: Sense Induced Flow - Active use of ambient flow by a deep-sea glass sponge

How flow moves through porous structures like sponges is a fluid dynamic problem that has challenged physical and biological scientists. Sponges possess biological pump cells that are known to drive water flow, and yet their porous bodies have often been proposed to take advantage of ambient currents passively. Here we focus on the ‘induced-flow’ theory which proposes that pipe-shaped structures can allow flow external to the tube to drive flow through the tube. This concept has been widely applied to both living systems and biogenic structures and particularly resonates with paleontologists who often give a poriferan-affinity to fossils with holes, assuming that the canals of sponges are inert. A modern understanding of sponge morphology and physiology however, shows sponges possess a sophisticated sensory system, even in the canals. Glass sponges (Hexactinellida) are an ideal group with which to re-examine the hypothesis because individuals have large oscula and have a well-studied sensory system that can cause feeding current arrests. Here we studied filtration and metabolism from glass sponges in their natural habitat on a glass sponge reef at 190m depth. We used custom oxygen and flow sensors to record oxygen removed per liter pumped over several tidal cycles, to test the hypothesis that the glass sponge Aphrocallistes vastus expends less energy to filter more water during higher ambient flow. We found that more water was filtered during periods of higher ambient current in only one of six individuals. However, all sponges arrested pumping independently of ambient currents, indicating they have control over pumping. We compared oxygen removal between low and high ambient flow during periods when sponges were pumping (high excurrent). Surprisingly, four of six sponges removed on average 30% less oxygen when the ambient current was high. This suggests a mechanism by which the sponge senses the increase in ambient flow rates and reduces the cost of filtration. The underlying mechanism by which the sponges sense the change in ambient current and control the flow through its body remains unknown, but may involve feedback from primary cilia at the osculum that are involved in flow sensing and dilation of canals in other sponges. Our experiments show that while sponges can take advantage of current-induced flow, the flow through these animals is controlled by their complex physiology. Overall these results imply that the feedback system in nerveless sponges functions in a manner similar to other animals formed by tubes.

流体如何在海绵等多孔结构中运动，是一道长期困扰物理与生物科学家的流体动力学问题。海绵拥有被认为可驱动水流的生物泵细胞，但其多孔躯体却常被认为可被动利用环境水流。本文聚焦“诱导流”理论：该理论提出，管状结构可借助管外外部水流驱动管内流体流动。这一概念已被广泛应用于生命系统与生物成因构造，尤其受到古生物学家的认同——他们常将带孔洞的化石归为具有多孔动物门（Porifera）亲缘关系的类群，默认海绵的管腔为惰性结构。然而，对海绵形态学与生理学的现代研究表明，即便在管腔中，海绵也拥有复杂的感官系统。玻璃海绵（Hexactinellida）是重新检验该假说的理想类群：这类生物拥有大型出水口（osculum），且其感官系统已被充分研究，可引发摄食水流停滞。我们于190米水深的玻璃海绵礁自然生境中，开展了玻璃海绵的滤食与代谢研究。通过定制的氧气与流量传感器，我们记录了多个潮汐周期内每升泵出水体的耗氧量，以此检验假说：大型玻璃海绵*Aphrocallistes vastus*在更高的环境水流条件下，过滤更多水体时消耗的能量更少。我们发现，仅6个受试个体中的1个在环境水流更强的时段过滤了更多水体。但所有海绵均独立于环境水流停止泵水，这表明它们可对泵水过程施加调控。我们对比了海绵处于泵水状态（即外排水流旺盛期）时，低与高环境水流条件下的耗氧量。令人意外的是，6个海绵中有4个在环境水流较强时，平均耗氧量降低了30%。这提示海绵可感知环境水流速率的提升，并借此降低滤食成本。海绵感知环境水流变化并调控体内水流的具体机制仍不明晰，但可能涉及出水口处的初级纤毛的反馈作用——这类纤毛在其他海绵中参与水流感知与管腔扩张。我们的实验表明，尽管海绵可利用水流诱导的流动，但流经其体内的水流仍受其复杂生理系统的调控。总体而言，这些结果意味着，无神经海绵的反馈系统运作方式与其他管状动物相似。