基于rDNA ITS序列分析莲塘湖萼花臂尾轮虫种群遗传结构的季节变化

对采自芜湖市莲塘湖水体中的萼花臂尾轮虫(Brachionus calyciflorus)夏季种群中的30个克隆(S1-S30)和秋季种群中的20个克隆(A1-A20)的rDNA ITS序列进行了分析;以十指臂尾轮虫B.patulus为外群,构建了50个克隆的NJ、MP和ME系统发生树。结果表明:三个系统树均支持将50个克隆分为两个支系;第一支系包括29个夏季采集的单元型(单元型S9除外)和1个秋季采集的单元型A2,第二个支系包括18个秋季采集的单元型(单元型A2除外)和1个夏季采集的单元型S9;两支系间ITS序列差异为5.1%-8.8%;它们应属于两个不同的姐妹种。夏季,莲塘湖水体中的萼花臂尾轮虫种复合体内以第一支系为主构成的姐妹种在相对丰度上占绝对优势,达29/30;而秋季则相反。上述结果表明:浅水湖泊中萼花臂尾轮虫种群密度的季节变动实际上主要在于各姐妹种相对丰度的季节变化;两姐妹种的种群遗传结构季节变化符合重叠模型。

Seasonal changes in the genetic structure of a Brachionus calyciflorus population in Lake Liantang based on ITS sequences

The ITS sequences of 30(S1-S30)and 20(A1-A20)Brachionus calyciflorus clones collected respectively in summer and autumn from Lake Liantang were analyzed;and using B.patulus as outgroup,the phylogenetic trees of Maximum-Parsimony(MP),Neighbor-Joining(NJ)and Minimum Evolution(ME)were constructured.All the three phylogenetic trees supported that 50 clones should be obviously divided into two different clades.The first clade included 29 haplotytes(except S9)collected in summer and 1 haplotyte(A2)collected in autumn,and the second one included 18 haplotytes(except A2)collected in autumn and 1 haplotyte(S9)collected in summer.The divergence of ITS sequence between the two clades was 5.1%-8.8%,and the two clades belonged to two sibling species.In summer,the sibling species composed of the first clade predominated in B.calyciflorus complex,with a higher abundance of 29/30;but the reverse was also true in autumn.The above-stated results indicated that the seasonal variation of B.calyciflorus population density in shallow lakes attribute principally to the seasonal variation of relative abundance of sibling species in B.calyciflorus complex,and the seasonal variation pattern of genetic structure of both the two sibling species populations can be described by the overlap model.