Collaborative Research: De Novo Evolution of Multicellularity in a Unicellular Volvocine Alga

地球上的生命既包括非常简单的有机体，也包括相当复杂的有机体。推动这项研究的中心问题是简单的生物体是如何进化成复杂的生物体的？由不止一个细胞组成的生物体(即多细胞生物体)的起源是生命历史上为数不多的重大事件之一，这些事件为更复杂的生物系统，如植物和动物，创造了新的进化机会。然而，对于进化生物学来说，理解这种复杂性如何以及为什么在某些谱系中增加仍然是一个重大挑战。多细胞进化带来的挑战，以及生物体内细胞之间分担劳动和合作机制的进化，构成了许多医学疾病的基础，是理解基因型与表型关系的基础。该项目还将开发新的课程材料，向高中生传授细胞分化和多细胞的挑战。这项研究的目标是在单细胞绿藻中实验进化多细胞莱茵衣藻。C.reinhardtii是一个已建立的模型系统，拥有一套完善的遗传工具。它在伏尔沃因藻类中的亲缘关系从只有一个细胞的物种到拥有数万个不同细胞类型的细胞的物种。在实验室中产生一种新的多细胞起源将使多细胞后代与其单细胞祖先直接进行比较。12个重复种群将在滤食性捕食者存在的情况下进化，这种情况下已知有利于多细胞。在这些实验过程中发生的遗传变化将被跟踪，以揭示多细胞的遗传基础和导致这些变化的进化过程。实验数据将与Volvocine藻类中多细胞进化的进化和遗传路线进行比较。最后，将评估环境诱导的发育变化在多细胞进化中的作用。

Life on Earth includes both very simple and rather complex organisms. The central question motivating this research is how do simple organisms evolve into complex organisms? The origin of organisms composed of more than one cell (i.e., multicellular organisms) was one of a few major events in the history of life that created new opportunities for more complex biological systems, such as plants and animals, to evolve. However, understanding how and why this kind of complexity has increased in some lineages remains a major challenge for evolutionary biology. The challenges posed by the evolution of multicellularity, in the evolution of mechanisms for sharing labor and cooperating among the cells within an organism, underlie many medical conditions and are foundational in understanding genotype to phenotype relationships. This project will also develop novel curriculum materials for teaching high school students about cellular differentiation and the challenges of multicellularity. The goal of this research is to experimentally evolve multicellularity in the single-celled green alga Chlamydomonas reinhardtii. C. reinhardtii is an established model system with a well-developed set of genetic tools. Its relatives among the volvocine algae range from species having single cells to those having tens of thousands of cells of different cell types. Generation of a novel origin of multicellularity in the lab will enable direct comparison of multicellular descendants to their unicellular ancestors. Twelve replicate populations will be evolved in the presence of a filter-feeding predator, conditions known to favor multicellularity. Genetic changes that occur over the course of these experiments will be tracked to reveal the genetic basis of multicellularity and the evolutionary processes giving rise to those changes. Experimental data will be compared with the evolutionary and genetic routes by which multicellularity evolved in the volvocine algae. Finally, the role of environmentally induced developmental changes in the evolution of multicellularity will be evaluated.