中国大陆鲫复合种遗传结构及不同生物型间的基因流研究

Carassius auratus complex is among the most economically important freshwater fish species in China, which consist of both sexually diploids and gynogenetically polyploids (triploids and tetraploids). In mainland China, a certain proportion of gynogenetically triploid C. auratus are fertile males, which make Carassius auratus complex to be a special case to vertebrates with typically biological significance. The studies based on mitochondrial DNA have found several distinct lineages in C. auratus complex and many mtDNA haplotypes were shared between diploids and polyploids within the same lineage. These results suggested that there are ongoing gene flows between polyploidy biotypes and diploidy biotypes. According to a few studies in which nuclear genome genetic structure of C. auratus complex was involved, triploidy biotypes probably originated from diploidy biotypes many times, which meant there were unidirectional gene flows from diploids to triploids. However, these studies didn't test whether there was reverse or even bidirectional gene flow between diploids and polyploids with more data. Given mtDNA genetic structure of C. auratus complex species was relatively well known, this project intends to investigate nuclear genome genetic structure of C. aurautus complex, and then elucidate the direction and extent of gene flow between different biotypes of C. aurautus complex. The results of this study will not only helped to properly protect and utilize the germplasm of C. aurautus complex, but also deepen our understandings about the biology of polyploid C. auratus, which will be guides to study sex-related biology using C. aurratus complex as a model.

鲫复合种(Carassius auratus complex)中既有两性生殖的二倍体,也有雌核发育生殖的多倍体(三倍体和四倍体),是我国最重要的经济鱼类之一。中国大陆分布的雌核发育三倍体鲫中有一定比例的可育雄性个体，是脊椎动物中的特例，有典型的生物学意义。基于线粒体DNA的研究表明鲫复合种中有多个分化明显的谱系,同一谱系内的二倍体和多倍体有许多共享的线粒体DNA单倍型,这一结果提示二倍体鲫与多倍体鲫间有持续的遗传交流。有涉及鲫核基因组遗传结构的研究推测三倍体可能多次起源于同一谱系的二倍体,即存在二倍体到三倍体单向的基因流,但却未考察是否存在反向或双向的基因交流。本项目拟在鲫复合种线粒体DNA谱系已比较清楚的基础上研究其核基因组遗传结构,进而阐明鲫复合种各种生物型间基因流的方向和程度。相关研究结果不仅有助于鲫复合种的资源保护与利用,也有助于以鲫复合种为模型开展性别相关生物学问题的研究。

鲫复合种(Carassius auratus complex)中既有两性生殖的二倍体,也有雌核发育的多倍体，是我国最重要的经济鱼类之一。基于线粒体DNA的研究表明鲫复合种中有多个分化明显的谱系，同一谱系内的二倍体和多倍体甚至共享许多的线粒体DNA单倍型。这一结果可能有两种解释：一是多倍体近期多次起源于二倍体鲫；二是多倍体鲫与二倍体鲫间有持续的遗传交流。由于多倍体行雌核发育生殖，缺乏有性生殖的遗传重组，此前的多数研究持前一种观点。本项目比较分析了鲫复合种线粒体DNA和核基因组遗传结构，并开展了人工繁殖实验，研究结果加深了对鲫复合种生殖与遗传规律的认识。本项目主要工作和结果如下：（1）、线粒体DNA分析结果除支持前人关于鲫复合种系统地理格局的主要成果外，发现以前被忽视的C7谱系在中国黑龙江流域有着较广泛的分布，其自然分布区很可能横跨亚洲大陆中纬度地区。研究中还发现C5谱系可能主要分布于长江流域中游。（2）、线粒体DNA和核基因组遗传结构研究结果均支持不同线粒体谱系间有显著的遗传分化，但是二倍体和三倍体间分化并不显著，支持两者间有持续的遗传交流。（3）、开展了二倍体和三倍体间的杂交实验，结果验证了前人关于二倍体雌与三倍体雄杂交可以获得存活子代的发现。但是不同于前人的研究，基因型检测结果支持子代是两性生殖而非雄核发育的产物，提示二倍体雌与三倍体雄交配可能是二倍体与三倍体间遗传交流的途径。两性生殖易获得重组的优秀后代，但是难以稳定遗传。雌核发育子代是母本的克隆，能够稳定遗传，却缺乏遗传重组。本项目的研究结果初步揭示了中国大陆鲫复合种遗传结构和可能的交流途径，为鲫品种选育过程中综合利用两性生殖和雌核发育的优势提供新的启示。