Collaborative Research: DMS/NIGMS2: Computational and Experimental Analysis of Choanoflagellate Hydrodynamic Performance - Selective Factors in the Evolution of Multicellularity

从单细胞原生动物祖先进化成多细胞动物是地球生命史上的一个关键转变。 Choanoflagellates是原生动物，与动物有共同的祖先。 它们可以是单细胞的，也可以通过细胞分裂形成多细胞集落，因此我们正在研究它们，以获得有关多细胞进化的见解。 对于通过自然选择在动物祖先中进化出的多细胞生物来说，影响生长，繁殖和生存的活动的表现对于群体来说比单细胞更好。 该项目将重点关注单细胞和多细胞choanoflagellates的活动，影响他们的健身性能之间的差异： 游泳、进食和避免捕食--所有这些都取决于生物体周围的液体流动。 该项目还将解决一个重要的生态问题。 领鞭毛虫和其他微小的原生动物以细菌为食，反过来又被小动物吃掉，它们是水生食物网中的关键一环。 许多原生动物是单细胞的，而另一些则形成多细胞群体，但单细胞与多细胞对游泳，进食和逃跑性能的影响尚未被理解。同时产生单细胞和多细胞形式的Choanoflagellates，使我们能够研究这些功能的表现在一个单一的物种的殖民地形成的影响。 单细胞后囊鞭毛虫具有卵圆形的细胞体和被微绒毛围成的单个鞭毛。细胞通过摆动鞭毛游动，鞭毛也会产生水流，将细菌带到捕获猎物的微绒毛的项圈上。我们将协调实验室实验与数学模型和计算机模拟，研究决定choanoflagellates的性能的水动力机制。 因此，从choanoflagellates了解到的单细胞与多细胞菌落的性能的原则可能会揭示影响水生原生动物的生态相互作用的机制，以及动物的进化起源。该项目还将为本科生和研究生以及博士后学者提供参与研究的机会。成功喂养和捕食者回避是表现的例子，可能是从单细胞进化到多细胞的重要选择因素。 我们的跨学科团队将协调实验室实验，数学建模和计算模拟，以研究游泳，喂养，并与捕食者的各种配置的单细胞与殖民choanoflagellates相互作用的流体动力学，以及海绵choanocytes的泵送和喂养。将开发模型，探测细胞形态，数量和安排，可以在系统的方式不同的影响不可能与真实的choanoflagellates。这些微尺度系统需要新的方法，捕捉细胞形态，几何形状的限制结构，动态附件，和脱离的细菌从choanoflagellate衣领，和化学和流体动力学信号提交给捕食者。正则化Stokeslets的方法将被提出来建模这些复杂的系统。实验室实验将使用的choanoflagellates物种，可以是单细胞的，并形成玫瑰花状菌落与鞭毛指向外，或形成杯形菌落，可以把里面出来，使鞭毛线杯，以及原生动物捕食者的choanoflagellates。微摄像将用于粒子跟踪测速的流场所产生的choanoflagellates，并测量游泳速度，喂养率，并与predators.This奖项的互动反映了NSF的法定使命，并已被认为是值得通过评估使用基金会的智力价值和更广泛的影响审查标准的支持。

The evolution of multicellular animals from a unicellular protozoan ancestor was a pivotal transition in the history of life on earth. Choanoflagellates are protozoans that share a common ancestor with animals. They can be unicellular or form multicellular colonies by cell division, so we are studying them to gain insights about the evolution of multicellularity. For multicellularity to have evolved via natural selection in the ancestors of animals, the performance of activities that affected growth, reproduction, and survival would have been better for colonies than for single cells. This project will focus on performance differences between unicellular and multicellular choanoflagellates of activities that affect their fitness: swimming, feeding, and avoiding predation – all of which depend upon the fluid flow around the organisms. This project also will address an important ecological issue. Choanoflagellates and other microscopic protozoans that eat bacteria and are in turn consumed by small animals are a critical link in aquatic food webs. Many protozoans are unicellular, while others form multicellular colonies, but the consequences to swimming, feeding, and escape performance of being single-celled versus multicellular are not yet understood. Choanoflagellates that produce both unicellular and multicellular forms permit us to study the effects of colony formation on the performance of these functions within a single species. A unicellular choanoflagellate has an ovoid cell body and a single flagellum surrounded by a collar of microvilli. The cell swims by waving its flagellum, which also creates a water current that brings bacteria to the collar of prey-capturing microvilli. We will coordinate laboratory experiments with mathematical models and computer simulations that study the hydrodynamic mechanisms that determine the performance of choanoflagellates. Thus, the principles learned from choanoflagellates about the performance of single cells versus multicellular colonies may shed light on mechanisms affecting ecological interactions of aquatic protozoans, as well as on the evolutionary origins of animals. The project will also provide opportunities for undergraduate and graduate students, and postdoctoral scholars to participate in the research.Feeding success and predator avoidance are examples of performance that might have been important selective factors in the evolution from single cells to multicellularity. Our interdisciplinary team will coordinate laboratory experiments, mathematical modeling, and computational simulations to study the hydrodynamics of swimming, feeding, and interacting with predators by unicellular versus colonial choanoflagellates of various configurations, and of pumping and feeding by sponge choanocytes. Models will be developed that probe the effects of cell morphology, number, and arrangement that can be varied in systematic ways not possible with real choanoflagellates. These microscale systems require novel methods that capture cell morphology, geometry of confining structures, dynamic attachment, and detachment of bacteria from choanoflagellate collars, and the chemical and hydrodynamic signals presented to predators. The method of regularized Stokeslets will be advanced to model these complex systems. Lab experiments will use species of choanoflagellates that can be unicellular and form rosette colonies with flagella pointing outwards, or that form cup-shaped colonies that can turn inside-out so the flagella line the cup, as well as protozoan predators on choanoflagellates. Micro videography will be used for particle-tracking velocimetry of flow fields produced by the choanoflagellates, and to measure swimming speeds, feeding rates, and interactions with predators.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.