两种鲿科鱼类在长江和珠江流域Cytb基因序列变异性分析

MITOCHONDRIAL CYTOCHROME B GENE SEQUNCE VARIATIONS OF TWO BAGRID FISHES IN CHANGJIANG RIVER AND ZHUJIANG RIVER

采用PCR技术获得了长江和珠江流域的两种科鱼类 1 1 37bpCytb基因的片段 ,进行了序列测定 ,并用Mega软件进行了序列分析。研究发现两种科鱼类的全序列从第十位碱基起有一个三联体密码子的缺失 ,推测为鲇形目鱼类Cytb序列所特有特征。黄颡鱼和大鳍种群间的序列差异分别为 0 .4 %和 1 .6 % ,介于一般淡水鱼类mtDNA种内序列的变异范围 ,而高于洄游鱼类序列变异。黄颡鱼属和属Cytb基因序列间的差异为 1 7.6 %— 1 8.0 % ,大大高于种间的序列差异率 ,也从分子水平上证实了二者属级分类单元的有效性。依据分子进化速率推测 ,长江和珠江两水系间大鳍的分歧时间为距今 2 7万年左右的更新世中晚期 ,黄颡鱼的分歧时间在距今 7万年左右的更新世末期。推测造成二者有着不同分歧时间的可能原因是 :大鳍属暖水性鱼类 ,在第四纪冰川期间 ,由于全球性气候变冷 ,大鳍退至长江以南 ,并在各水系间产生隔离 ,各自独立分化至今。而黄颡鱼具有很强的适应性 。

MtDNA cytochrome b gene sequence variations of samples of two bagrid fishes from Changjiang and Zhujiang Rivers were studied in the present paper. 1137 bp sequences were obtained through PCR amplifications.Sequence analysis was conducted using MEGA program with the sequence of the common carp downloaded from GenBank for comparison.The results showed that there is a codon deletion in cytochrome b gene of the two bagrid species at the tenth nucleotide position compared with that of the common carp, which could be a common character for all catfishes. The intraspecific sequence divergences of Pelteobagrus fulvidraco and Mystus macropterus were 0.4% and 1.6% respectively,which were in the range of freshwater fishes ,but higher than those of anadromous fishes.The sequence differences between P. fulvidraco and M. macropterus were from 17.6% to 18.0%, which were much higher than the intraspecific variations. Inferred from the molecular evolution rate,the divergent time of M. macropterus in Changjiang and Zhujiang rivers was about 270 thousand years ago during middle and late Pleistocene ,and that of P.fulvidraco was 70 thousand years ago in the late Pleistocene.The reason that the two bagrid fishes in Changjiang and Zhujiang Rivers have different divergent times might be that M. macropterus is warm fresh water fishes,and they were limited to the south of Changjiang River in China during the middle and late Pleistocene glacial period and differentiated in different water systems till now; while P.fulvidraco is a widespread species and can adapt to different environments, thus exchanges among P.fulvidraco populations might have occurred among different water systems during the Quaternary glacial period.