Collaborative Research: Evolution of Multicellularity: Fluid Mechanics of Feeding by Unicellular vs. Multicellular Choanoflagellates

合作研究：多细胞性的进化：单细胞与多细胞领鞭毛虫摄食的流体力学

• 批准号: 1147215
• 负责人: Mimi A Koehl
• 金额: $ 34.74万
• 依托单位: University of California-Berkeley
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2012
• 资助国家: 美国
• 起止时间: 2012-05-01 至 2016-10-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1147215&HistoricalAwards=false
• 关键词: Collaborative; Research; Evolution; Multicellularity; Fluid

The evolutionary origin of multicellular animals from a single-celled protozoan ancestor represents a pivotal transition in life's history and one of its greatest unsolved mysteries. Recent genetic studies have shown that the most primitive animals (sponges) are very closely related to a group of protozoans called choanoflagellates. A choanoflagellate cell swims by undulating a single flagellum and captures food (bacteria) from the surrounding water on a collar of microvilli (hair-like protrusions of the cell surface) that rings the flagellum. Some single-celled choanoflagellates can be induced to form multicellular colonies via cell division. One such species that lives in estuaries, Salpingoeca rosetta, is used to study the evolution of multicellularity. For multicellularity to evolve, there must have been a selective advantage to being multicellular, but since both unicellular and colonial choanoflagellates still exist today, there may be different environmental conditions under which single-celled or multicellular forms perform better. One important aspect of performance that affects choanoflagellate survival and reproduction is feeding on bacterial prey. Marine habitats can differ in the size, spacing, and richness of patches of bacteria. This study uses S. rosetta to study the consequences of being multicellular vs. unicellular to foraging success, and to discover the mechanisms responsible for differences in performance. The objectives are: 1) to quantify the swimming behavior of unicellular vs. colonial S. rosetta in environments in which bacteria are unevenly distributed, to determine if and how choanoflagellates aggregate in patches of high prey concentration; 2) to determine the feeding rates of unicellular vs. colonial S. rosetta for a range of bacterial prey concentrations; and 3) to study the fluid mechanics of water current production and prey capture by S. rosetta, to elucidate how being part of a colony alters the feeding current, and the mechanisms and effectiveness of prey capture. The diverse expertise of a multidisciplinary team will be focused on these objectives: Koehl (fluid dynamics of organisms), King (molecular evolution of choanoflagellates), Stocker (biophysics and ecology of microscopic aquatic organisms), and Fletcher (advanced optical techniques for imaging microscopic organisms). This study not only explores the role of foraging as a selective factor in the evolution of multicellularity, which set in motion all subsequent animal evolution, but also has ecological significance. Protozoans, both unicellular and colonial, play an important role in aquatic food webs. This project is the first to study, within a single protozoan species, the effects of being uni- vs. multicellular to foraging by these ecologically-important organisms.This project will provide research training for graduate students in a project involving both physics and biology, helping them develop skills for collaboration across disciplines. The microfluidics system developed for this project will be useful for studying other microscopic organisms in patchy environments, and our robotic flagellum is a prototype for future studies of undulatory swimming.

多细胞动物从单细胞原生动物祖先进化而来的起源代表着生命历史上的一个关键转变，也是其最大的未解之谜之一。最近的遗传学研究表明，最原始的动物(海绵)与一群名为脊椎动物的原生动物关系密切。后鞭毛细胞通过波动单个鞭毛来游泳，并在环绕鞭毛的微绒毛(细胞表面的毛状突起)的领子上从周围的水中捕获食物(细菌)。一些单细胞的尾鞭毛虫可以通过细胞分裂诱导形成多细胞集落。生活在河口的这样一个物种，Salpingoeca Rosetta，被用来研究多细胞的进化。对于多细胞的进化，多细胞必须有选择性的优势，但由于单细胞和集群节节藻今天仍然存在，可能存在不同的环境条件，在不同的环境条件下，单细胞或多细胞形式的表现更好。影响脊椎动物生存和繁殖的一个重要方面是捕食细菌猎物。海洋栖息地可以在细菌斑块的大小、间距和丰富度上有所不同。这项研究使用S.Rosetta来研究多细胞和单细胞对觅食成功的影响，并发现导致性能差异的机制。其目的是：1)量化单细胞和集群的Rosetta在细菌分布不均匀的环境中的游泳行为，以确定节鞭毛虫是否以及如何聚集在高猎物浓度的斑块中；2)确定在一定细菌猎物浓度范围内，单细胞和集群的S.Rosetta的摄食率；以及3)研究S.Rosetta产生水流和捕获猎物的流体力学，以阐明作为集群的一部分如何改变摄食电流，以及猎物捕获的机制和有效性。一个多学科团队的不同专业知识将集中在这些目标上：Koehl(生物的流体动力学)、King(脊椎动物的分子进化)、Stocker(微型水生生物的生物物理和生态学)和Fletcher(为微观生物成像的高级光学技术)。这项研究不仅探索了觅食作为选择性因素在多细胞进化中的作用，启动了所有后续的动物进化，而且具有生态学意义。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。这个项目是第一个在单个原生动物物种中研究单细胞和多细胞对这些具有生态重要性的生物觅食的影响。这个项目将为研究生提供一个涉及物理和生物学的项目的研究培训，帮助他们发展跨学科合作的技能。为该项目开发的微流体系统将有助于研究片状环境中的其他微生物，我们的机器人鞭毛是未来波动游泳研究的原型。