五种鲟鱼线粒体控制区异质性和系统发育分析

利用保守引物得到五种鲟鱼的线粒体DNA（mtDNA）控制区（D-loop）全长，长度在795~813 bp。序列中包括了CBS（conserved sequence block）和TAS（termination-associated sequence）区域。利用最大似然法、最大简约法和贝叶斯法构建了系统发育树，发育树分成两枝，呈现明显的生物地理分布。分析表明，现有的鳇属鱼类不是单系群起源。五种鲟鱼D-loop序列都存在长度和数目不等串联重复序列，长度在78~82 bp之间，重复序列拷贝数在4~6次不等，因此造成了mtDNA广泛的异质性现象。不同种类的重复序列单元十分相似，达氏鳇和史氏鲟重复序列单元相似度为82.93%，西伯利亚鲟和俄罗斯鲟重复序列单元相似度为90.59%。在串联重复序列后是一段不完全重复序列。通过与已有同种的重复序列比对发现不同鲟鱼重复序列相同，不同地理区域相同物种的重复序列可能发生过分子内重组。这些表明重复序列在鲟鱼进化上具有相关意义，推测重复序列可能产生在种分化前，重组发生在种分化后。

Heteroplasmy in mtDNA Control Region and Phylogenetics of Five Sturgeons

The sequences of the control region (D-loop) of mitochondrial DNA ( mtDNA) were obtained from five species of sturgeon. The sequences obtained had lengths between 795-813 bp. The motifs of the conserved sequence block (CBS) and termination-associated sequence (TAS) were identified in the sequences. Examination of the molecular phylogeny using maximum likelihood, maximum parsimony and Bayesian analysis shows that sturgeons form two clades representing biogeographic distribution, and the Huso is not monophyletic. Heteroplasmy in 150 fishes was due to a variable number of tandem repeats. Length of the central repeat units ranges from 78 to 82 bp with repeat sequence copies between four and six. The repeat units, followed by an imperfect repeat unit, are in high similarity between species, with 82.93% between Amur sturgeon and starlet and 90.59% between Siberian sturgeon and Russian sturgeon. Furthermore, comparing with other repeat sequences published, different species have the same repeat unit and intramolecular recombination event may happen in the repeat unit. All of these indicate that the repeat units are related to the evolution of sturgeon and arose prior to species divergence after which recombination happened.