Hydrodynamic functionality of the lorica in choanoflagellates
Hydrodynamic functionality of the lorica in choanoflagellates
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DOI：
10.1098/rsif.2018.0478
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发表时间：
2019-01-01
影响因子：
3.9
通讯作者：
Walther, Jens H.
中科院分区：
文献类型：
--
作者：
Asadzadeh, Seyed Saeed;Nielsen, Lasse Tor;Walther, Jens H.
领鞭毛虫是单细胞真核生物，在水生栖息地中普遍存在。它们有一个鞭毛，可以产生流向由从细胞延伸的过滤丝组成的套环过滤器的流动。在一个常见的类群，即领鞭毛虫中，细胞悬浮在一个复杂的篮状结构中，即 lorica，其功能仍然未知。在这里，我们使用计算流体动力学来探索 lorica 可能的流体动力学功能。我们使用领鞭毛虫 Diaphaoneca grandis 作为模式生物。据推测，lorica 的功能是防止再过滤（水流再循环）并增加阻力，从而增加进食速度并降低游泳速度。我们没有发现这些假设的支持。相反，菱形动物遇到活动猎物的几率要低得多。 lorica的存在不会影响平均游泳速度，但会抑制细胞的横向运动和旋转。如果没有洛里卡，细胞在游泳时会左右摇晃。鞭毛的跳动产生的不稳定流动会导致通过领式过滤器的反向流动，这可能会在捕获的猎物被运送到细胞体进行吞噬时冲走。 lorica 大大减少了这种流量，因此它有可能提高捕获效率。这可能是lorica的主要适应价值。
Choanoflagellates are unicellular eukaryotes that are ubiquitous in aquatic habitats. They have a single flagellum that creates a flow toward a collar filter composed of filter strands that extend from the cell. In one common group, the loricate choanoflagellates, the cell is suspended in an elaborate basket-like structure, the lorica, the function of which remains unknown. Here, we use Computational Fluid Dynamics to explore the possible hydrodynamic function of the lorica. We use the choanoflagellate Diaphaoneca grandis as a model organism. It has been hypothesized that the function of the lorica is to prevent refiltration (flow recirculation) and to increase the drag and, hence, increase the feeding rate and reduce the swimming speed. We find no support for these hypotheses. On the contrary, motile prey are encountered at a much lower rate by the loricate organism. The presence of the lorica does not affect the average swimming speed, but it suppresses the lateral motion and rotation of the cell. Without the lorica, the cell jiggles from side to side while swimming. The unsteady flow generated by the beating flagellum causes reversed flow through the collar filter that may wash away captured prey while it is being transported to the cell body for engulfment. The lorica substantially decreases such flow, hence it potentially increases the capture efficiency. This may be the main adaptive value of the lorica.