中国沿海紫蛤属的系统发育

紫蛤属(Sanguinolaria)贝类具有很高的经济价值,长期以来却存在着物种鉴定错误、种名使用混乱、同物异名等一系列问题,关于其系统分类和演化问题的研究较少。为探究中国沿海紫蛤属的系统发育关系,本研究利用两个线粒体基因(COI和16S rRNA),以及两个核基因(H3和28S rRNA)的部分序列,对采自中国沿海紫蛤属3亚属9种紫蛤61个个体进行系统发育分析。基于4个基因片段联合数据集T12(剔除COI第三位密码子位置)构建系统发育树。结果表明,两个线粒体基因片段GC含量明显低于AT含量,表现出对AT偏斜,两个核基因表现出对GC的偏斜。4个基因片段(COI、16S rRNA、H3和28S rRNA)的颠换与转换比值分别为5.073、3.042、1.564和1.480,均远高于系统分析的临界值0.4,能够提供有效的系统发育信息。基于4个基因片段的遗传多样性分析表明,9种紫蛤均具有较高的核苷酸多样性(Pi0.05)与单倍型多态性(Hd0.5)。基于COI基因片段的紫蛤属种内遗传距离为0~0.016,种间的平均遗传距离为0.087~0.331,其中卵紫蛤(Sanguinolaria ovalis)与中国紫蛤(Sanguinolaria chinensis)遗传距离最小,仅为0.087。利用最大似然法(maximum likelihood,ML)和贝叶斯法(Bayesian inference,BI)构建的系统发生树拓扑结构一致,分化为3大支,与形态学分类的三个亚属分别对应。中国紫蛤和卵紫蛤在系统树上首先聚为一支,表明其亲缘关系最近。本研究结果阐明了中国沿海紫蛤属贝类的遗传多样性及其系统演化关系,为紫蛤属贝类种质资源的保护及可持续利用提供了科学依据。

Phylogenetic relationships among Sanguinolaria species in the coastal waters of China

Fragments of the mitochondrial gene (COI and 16S rRNA) and the nuclear marker (H3 and 28S rRNA) regions are suitable for phylogenetic relationship analysis. The phylogenetic relationships among nine Sanguinolaria species (Sanguinolaria acuta, S. chinensis, S. diphos, S. ovalis, S. virescens, S. elongata, S. minor, S. olivacea, and S. tchangsii) collected from the coastal areas of China was analyzed through the sequencing of COI, H3, 16S rRNA, and 28S rRNA genes. The two mitochondrial genes, COI and 16S rRNA, had an obvious AT-skewness, and their GC content were 41.17% and 41.01%, respectively, showing a certain degree of base preference. The overall transition/transversion bias of the four fragments (COI 5.073, 16S rRNA 3.042, H3 1.564, and 28S rRNA 1.480) were much higher than the critical value (0.4), which could offer effective phylogenetic information. As the genetic diversity parameters of all four markers in nine Sanguinolaria species had higher values (Pi<0.05, Hd<0.5) than most bivalve species, it is suggested that the Sanguinolaria species may have long history in the localities, and sufficient phylogenetic information. Among the nine Sanguinolaria species, the genetic average distances based on the COI gene were 0.087-0.331, and the genetic distances within species were 0-0.016. The minimum genetic distance was between S. ovalis and S. chinensis, which was much higher than the average value (0.005) between most species of bivalves. The saturation of the nucleotide substitution process in the four markers was calculated as well. The third codon positions of the COI gene''s transition and transversion substitutions reached the point of saturation, which means that the third codon positions of the COI gene could not provide effective information. The combined data set T12, including the four molecular markers without the third codon positions of COI, totaled 1555 bp in length. Phylogenetic trees constructed by the Maximum Likelihood (ML) and Bayesian Inference (BI) methods were consistent, and cluster analysis based on the data set T12 showed three separate lineages, corresponding to three morphologically defined subgenera:Hainania, Nutallia, and Psammotaea. Combining morphological and molecular evidence, the results support that S. ovalis and S. chinensis has the closest phylogenetic relationship. The study sheds light on the genetic diversity and phylogenetic relationship of Sanguinolaria species occurring along the coast of China, which may be useful in genetic resource protection and sustainable use.