中国水域瓶鼻海豚的mtDNA控制区序列变异性分析

VARIABILITY OF THE MITOCHONDRIAL DNA CONTROL REGION OF BOTTLENOSE DOLPHINS(GENUS:TURSIOPS)IN CHINESE WATERS

测定了 30头中国水域瓶鼻海豚 (Tursiopssp .)mtDNA控制区 5′端 4 2 4bp的序列 ,结合已发表的中国水域其它瓶鼻海豚的mtDNA控制区序列 ,共发现 5 4个变异位点 ,定义了 37种单元型。中国水域瓶鼻海豚的两个形态型之间没有共享单元型 ,且具有 8个鉴别位点。基于最大似然法和邻接法的系统发生分析均把单元型聚类为分别代表两个形态型的支系。形态型之间的核苷酸歧异度为 5 5 8% ,超过了其它海豚类种间的序列歧异水平 ,支持把这两个形态型划分为两个独立的种 ,即T .truncatus和T .aduncus的观点。虽然两种瓶鼻海豚的分布区在台湾海峡一带出现重叠 ,但相互之间缺乏基因流动 。

Two distinct morphotypes of bottlenose dolphins ( Tursiops sp.) in Chinese waters have been recently referred to as T. truncatus and T. aduncus. However, the genetic composition and divergence of bottlenose dolphins in Chinese waters is not clear. 424 base pairs (bp) of the mitochondrial control region collected from 30 bottlenose dolphins from the Yellow and East China Seas, the Taiwan Strait and the Gulf of Beibuwan were sequenced. Combined with previously published mtDNA control region sequences of bottlenose dolphins from Chinese waters, 54 variable sites were determined and 37 haplotypes were identified. No shared haplotypes were found between two morphotypes, and eight fixed diagnostic site differences separate the two morphotypes. Phylogenetic relationships among haplotypes were determined using the maximum likelihood method and the neighbor joining method. Maximum likelihood analysis was performed using the Phylogenetic Inference Package (PHYLIP) version 3 5c. The distance matrix for neighbor joining analysis was generated using the Tamura Nei Gamma distance method of the Molecular Evolutionary Genetic Analysis (MEGA). Neighbor joining analysis was also performed using MEGA with 500 bootstraps. The average number of substitutions per site within groups (nucleotide diversity) and between groups (nucleotide divergence) were estimated using DnaSP. Haplotypic diversity for the two morphotypes of Chinese waters was also estimated. Reconstruction of the phylogenetic relationships among haplotypes divided the 37 haplotypes of bottlenose dolphins into monophyletic clades representing the two morphotypes. The average nucleotide divergence between the two morphotypes is 5 58%, which is about five times greater than between Delphinus species (1 09%). These support the conclusion that the two morphotypes of bottlenose dolphins in Chinese waters represent distinct species, i.e. T. truncatus and T. aduncus. Net nucleotide divergence between the two species was 3 79%. As the substitution rate for the cetacean mtDNA control region has been estimated to be 0 5% per million years, the two species probably diverged about 7 5 million years ago (Mya). Although the distribution of the two species overlap in the Taiwan Strait (and maybe adjacent waters), there is no genetic interchange between them, indicating reproductive isolation. In order to conserve more genetic diversity of Tursiops in the Chinese waters, the two species should be treated as independent conservation management units in conservation planning.