Functional Consequences of Being Multicellular: Predation by Protozoans on Unicellular vs. Multicellular Choanoflagellates

动物的身体是由许多细胞组成的，但动物的祖先是单细胞有机体(原生动物)。生命进化的关键一步是从单细胞到多细胞的转变。与动物最接近的原生动物近亲是水生的“尾鞭毛虫”，它们是单细胞的，但也可以形成多细胞的群体。对于多细胞的进化，动物祖先的群体必须比单独的细胞更好地发挥了影响它们生存的功能。这项研究考察了单细胞或多细胞脊椎动物是否能够更好地避免被原生动物捕食者吃掉，以及相关的机制。这个位于生物学和物理学(水生捕食者和猎物如何相互作用的流体力学)交界处的项目将为来自不同专业的本科生团队提供实践研究经验，并让他们参与跨学科研究，这一点很重要，因为未来在科学和技术方面的许多发现将在不同领域之间的交界处取得。公众宣传包括一个互动的在线网站，公民科学家可以在那里计算不同类型的捕食者对单细胞和多细胞脊椎动物的捕食率。私人投资机构与妇女和阅读困难者的合作将鼓励在科学和技术领域取得成功。将开发一种新的微流控系统，以确定捕食者-猎物相互作用(通常在静止水中研究)的性能和机制如何受到微观游泳者在自然、湍急的水流中经历的真实波动剪切模式的影响。该系统对研究自然界中其他相互作用的水生微生物具有一定的参考价值。原生动物，无论是单细胞的还是群居的，在水生食物网中都扮演着重要的角色。鞭毛虫是动物最接近的原生动物近亲，将被用来研究单细胞原生动物与多细胞原生动物抵抗捕食的潜在机制。关于脊椎动物的数据还将使人们能够明智地推断捕食作为多细胞进化中的一个选择性因素可能起到的作用。多细胞动物起源于单细胞原生动物，代表着生命历史上的一个关键转变。这项研究的重点是抵抗被原生动物捕食者(在动物进化之前，软鞭毛虫上的捕食者是其他原生动物)。研究目标是：1)量化单细胞和集群节鞭毛虫在避免原生动物捕食者使用不同猎物捕获模式进行捕食方面的性能差异；2)阐明捕食者和集群节鞭毛虫猎物之间相互作用的流体动力学，以确定导致性能差异的机制；3)确定原生动物在自然界湍急水流中遇到的波动剪切如何影响单细胞与集群猎物与捕食者的相互作用。捕食者、猎物和流动标记微珠的高速视频显微摄影将记录脊椎动物与不同原生动物捕食者的相互作用。数字化的原生动物轨迹可以计算相遇和捕食成功率，以及行为互动。粒子跟踪测速仪将量化捕食者和猎物产生的瞬时流场，以及它们相互作用期间的水动力信号。一项新的贡献是微流体技术的发展，以确定捕食者-猎物相互作用的机制(通常在静止水中研究)如何受到微观游泳者在湍流环境中经历的真实波动剪切模式的影响。

Animal bodies are made up of many cells, but the ancestors of animals were single-celled organisms ("protozoans"). A pivotal step in the evolution of life was the transition from being unicellular to becoming multicellular. The closest protozoan relatives of animals are aquatic "choanoflagellates", which are unicellular but can also form multicellular colonies. For multicellularity to evolve, colonies of animal ancestors must have performed functions affecting their survival better than did solitary cells. This study examines whether unicellular or multicellular choanoflagellates are better able to avoid being eaten by protozoan predators, and the mechanisms involved. This project at the interface between biology and physics (hydrodynamics of how aquatic predators and prey interact) will give teams of undergraduate students from different majors hands-on research experience and will involve them in interdisciplinary research, which is important because many future discoveries in science and technology will be made at interfaces between different fields. Public outreach includes an interactive online site where citizen scientists can calculate the predation rates on unicellular and multicellular choanoflagellates by different types of predators. Work with women and dyslexics by the PIs will encourage success in science and technology fields. A novel microfluidic system will be developed to determine how performance and mechanisms of predator-prey interactions (usually studied in still water) are affected by realistic patterns of fluctuating shear that microscopic swimmers experience in natural, turbulent water flow. This system will be useful for studying other aquatic microoganisms interacting with each other in nature. Protozoans, both unicellular and colonial, play important roles in aquatic food webs. Chonaoflagellates, the closest protozoan relatives of animals, will be used to study mechanisms underlying resistance to predation by uni- vs. multicellular protozoans. Data about choanoflagellates will also enable informed inferences about the possible role of predation as a selective factor in the evolution of multicellularity. The origin of multicellular animals from unicellular protozoans represents a pivotal transition in life's history. This study focuses on resistance to being eaten by protozoan predators (before animals evolved, predators on chonaoflagellates were other protozoans). Research goals are to: 1) quantify performance differences between unicellular and colonial choanoflagellates in avoiding predation by protozoan predators using different modes of prey capture; 2) elucidate fluid dynamics of interactions between predators and choanoflagellate prey to identify mechanisms underlying performance differences; 3) determine how fluctuating shear encountered by protozoans carried in turbulent water flow in nature affects interactions of unicellular vs. colonial prey with predators. High-speed videomicrography of predators, prey, and flow-marking microbeads will record interactions of choanoflagellates with different protozoan predators. Digitized protozoan trajectories enable calculation of encounter and predation success rates, and behavioral interactions. Particle tracking velocimetry will quantify instantaneous flow fields produced by predators and prey, and hydrodynamic signals during their interactions. A novel contribution is development of microfluidic techniques to determine how mechanisms of predator-prey interactions (usually studied in still water) are affected by realistic patterns of fluctuating shear that microscopic swimmers experience in turbulent ambient water flow.