大鳍鱊基于细胞色素b基因序列的遗传变异及生物地理过程

GENETIC DIVERSITY AND BIOGEOGRAPHICAL PROCESS OF ACHEILOGNATHUS MACROPTERUS REVEALED BY SEQUENCE VARIATIONS OF MITOCHONDRIAL CYTOCHROME b GENE

对采集于长江水系、黑龙江水系及海南岛的36尾大鳍(Acheilognathus macropterus)的细胞色素b基因序列进行了研究分析。发现有须个体和无须个体在分子系统树中处于混合分布状态,各个体相互间遗传变异远小于与外类群(A.chankaensis、A.tokinensis)间差异,统计了其主要形态度量数据,也显示各主要性状数据无显著差异,结果均支持有须个体和无须个体(曾经被鉴定为A.taenianalis)为同一物种,A.taenianalis为A.macropterus的同物异名。序列分析显示,36个个体明显聚合成5个大的分支,其中clade1分支全部由黑龙江水系类群组成,clade5分支由海南岛的1个个体组成,长江水系的所有个体分散在clade2、clade3、clade4这三个分支中,显示出一定的地理相关性。在clade2、3、4中,clade2包括了长江上游的5个个体和长江中游的2个个体,同时还包括了黑龙江的2个个体;clade3包括了中游的2个个体;clade4包括了中游的12个个体,三个分支间又存在明显的遗传变异率(均>5%),从21个个体在三个分支中的分布情况来看,三者间这种较大的遗传变异率不能由地理隔离解释,故推测,造成同一水系的A.macropterus间出现较明显遗传分化的原因可能与其特殊的性选择生殖方式有关,该生殖方式限制了不同生殖集群间同种鱼类的基因交流。基于系统分支图,计算了各分支间的遗传距离,由结果推测大鳍的生物地理过程为:海南岛水系类群同大陆类群较早产生隔离,黑龙江水系类群由长江水系类群在晚近时期向北扩散形成。

In the present study, thirty-six individuals of Acheilognathus macropterus were collected from the Heilongjiang River, the Changjiang River, and the Nandujiang River. Partial mitochondrial cytochrome b gene region（636 base pair）was sequenced to these samples and 22 haplotypes were found. With A. chankaensis and A. tokinensis as outgroups, their relationships were analyzed. The p-distances were calculated with Mega software, and molecular phylogene-tic tree was constructed using the neighborjoining（ N J）method. Proportions of main morphological characters were compared as well. P-distances showed that the genetic differences in A. rnacropterus samples were much smaller than those between these samples and the outgroups. Molecular phylogenetic tree showed that samples with barbels and those without barbels were intermingled. There was no distinct difference in proportions of morphological characters. The results suggested that samples with barbels and those without barbels（ formally identified as A. taenianalis）are the same species, A. taenianalis is a junior synonyms of A. macropterus. The thirty-six individuals were grouped into 5clades, and the positions of the samples in the clades were corresponded with their geographical distributions. Among the 5 clades, clade 1 and clade 5 included specimens from Heilongjiang River and Nandujiang River respectively. The specimens from Changjiang River scattered into clades 2,3, and 4, and there were distinct genetic differences （ 〉 5 % ） among them. Interestingly, the distributions of the 21 samples in these three clades were not correlated to their geographical distributions. It is postulated that these genetic differences were due to bitterling＇ s mate choice, the prozygotic isolation. The genetic differences between the fish from Nandujiang River and those from the mainland indicated they were separated early. However, the small genetic differences among the samples and their positions of the fish from Heilongjiang River in the molecular phylogenetic tree indicate that fish from Heilongjiang River might disperse from Changjiang River very late.