单细胞真核绿藻在动物细胞内共生是进化生态学、进化生物学和细胞生物学等领域具有较高科研价值的特殊生物学现象，其中动物-单细胞真核绿藻共生体的生物学意义已经较为明确，但该类共生体的起源时间及进化机制目前仍未阐明。动物-绿藻共生体中，动物体为宿主，共生绿藻在进化上是后来进入动物细胞的，因此对共生绿藻的起源及动物宿主与共生绿藻协同进化机制的研究可能有助于动物-绿藻共生体起源机制的探讨。基于此，本课题拟在对我国淡水无脊椎动物类群中的动物-绿藻共生体多样性调查的基础上，运用分子系统学方法、基于不同动物宿主体内的共生绿藻及同一动物宿主不同地理种群的共生绿藻两个背景探讨不同来源共生绿藻的分子系统发生关系以及相应动物宿主间分子系统发生关系，以期对动物共生绿藻的起源及动物宿主与共生绿藻协同进化的分子机制进行综合分析和评价，为动物-绿藻共生体的起源和进化研究提供基础资料。

The symbiotic system consisting of freshwater invertebrate and unicellular eukaryotic green algae is a special biological phenomena which has a high scientific value in the field of evolutionary ecology, evolutionary biology and cell biology. So far, the biological significance of symbiont consisting of animal and unicellular eukaryotic green algae have been understood, while the time of its origin and its evolution mechanism have been unclear. In animal-algae symbiont, the animal is the host, symbiotic green algae entered later animal cell in evolution, thus related study on the origin and phylogenetics of symbiotic green algae and the mechanism of coevotion between symbiotic unicellular eukaryotic green algae and host animals should contribute to explore the origin and formation mechanism of animal-algae symbionts. Therefore, our scientific research item will first investigate the diversity of symbiont consisting of freshwater invertebrates and unicellular eukaryotic green algae in China, and based on this, molecular phylogenetic relationship among different symbiotic green algae as well as among relevant host animals would be studied respectively under two different backgrounds of symbiotic green algae in different animal hosts which exist at the same habitat and symbiotic green algae in different geographical populations of the same animal host. In a word, the aim of our item is to make comprehensive analysis and evaluation on molecular phylogeny, origin and evolution of symbiotic unicellular green algae and molecular mechanism of coevolution between host animal and symbiotic green algae, and lay a foundation for the study on the origin and evolution of animal-green algae symbiont.