采用DNA序列分析方法,分析拟平鳅不同地理种群间的遗传变异和亲缘关系.共检测了12条水系87尾拟平鳅的mtDNA控制区序列,在477 bp片段中有95个核苷酸变异位点,其中39个单个多态位点,56个简约信息位点.系统发育分析(NJ)结果显示,华南西部沿海地区拟平鳅20个单倍型分成3支;分支Ⅰ由广东西部独立入海水系和珠江水系的种群组成,分支Ⅱ由广西东部独立入海水系和海南岛昌化江的种群组成,而海南岛的万泉河和南渡江种群聚合成分支Ⅲ.表明海南岛不同水系的拟平鳅已经发生了遗传分化,一部分与广西的种群相似,另一部分是海南特有的.3个分支内的变异率(0.583%～1.775%)都明显小于各分支间的变异率(4.205%～5.715%),也远小于各分支与外类群间的变异率(11.825%～13.73%).说明华南西部沿海和海南岛的拟平鳅已分化成3个在遗传上有明显差异的群.基于现在的地理格局,研究曾经假设华南西部沿海独立水系种群与珠江水系种群的关系较密切,而与海南岛种群的关系较疏远.分子变异分析(AMOVA)表明,大部分的变异(65.04%)分布于地理区内种群间,而地理区间的变异仅占2.24%,与假设不符.表明12条水系拟平鳅mtDNA控制区序列的遗传分化可能主要是由于第三纪水系的隔离,而不是第四纪冰后期海南岛与大陆的分离所致.而第四纪盛冰期低海平面所造成的陆连,使相互分离的水系有机会连接,因此,海南岛昌化江种群与广西沿海独立水系种群关系密切,珠江水系种群保持与广东西部沿海独立水系种群的密切关系.而琼中海峡这个地理屏障形成的时间还不够长久,并没有成为有效的生殖屏蔽.AMOVA分析结果与上述NJ分析中各个分支之内的分子变异非常小的结果一致.%This study investigated population genetics and phylogenetics of Uniparhomaloptera disparis (Cypriniformes: Homalopteridae) among river drainages on Hainan Island and in coastal western South China, using nucleotide sequences in the mtDNA control region. Samples were taken from 3 major river systems on Hainan Island (Province), 2 major branches of the Pearl River system in Guangdong Province, and 7 independent coastal river systems in Guangdong and Guangxi Provinces. Hainan Island and coastal western South China were connected at the last glacial maximum about 10 thousand years ago. This study thus contributes to the understanding of phylogeography of different fishes from Hainan Island and the South China mainland. A total of 87 individuals from these 12 drainages were used in sequencing; we found 95 variable nucleotide sites among 477 base pairs, with 39 singleton sites and 56 parsimoniously informative sites. Neighbor-joining ( NJ) analysis with 20 haplotype nucleotides in the control region revealed 3 monophyletic clades. The Pearl River system and the independent coastal drainages in western Guangdong Province are closely related (clade I) ; the independent coastal drainages in eastern Guangxi Province group tightly with the Changhuajiang River on Hainan Island (clade II); the Wanquanhe and Nandujiang River drainages on Hainan Island form a lineage distinctly separate from the others (clade III). This indicates that populations of L disparis on Hainan Island are genetically differentiated into 2 lineages, one similar to those in Guangxi Province, and the other unique. The variation within a clade (0.583% - 1. 775% ) was much lower than that between clades (4. 205% -5. 715% ) or that between clades and outgroups (11.825% -13.73%), demonstrating that L disparis in these 12 drainage systems in coastal western South China and Hainan Island has divided into 3 genetically distinguishable groups. Analysis of molecular variance ( AMOVA) revealed that most of the genetic variation resided among populations within a geographic region (65.04% ) with little variation between geographic regions (2.24% ), rejecting our null hypothesis based on current disjunct geography that populations from the independent drainages in coastal western South China were closely related to those from the Pearl River but distantly related to those from Hainan Island. Variation in the mtDNA control region may have occurred due to drainage separation by montane uplift in the Tertiary, and cannot postglacial disjunction of Hainan Island from the mainland in the Quaternary. This geographic barrier has not existed long enough to effect reproductive isolation, leaving close relationships of populations from the Changhuajiang River on Hainan Island with those from the independent coastal drainages in eastern Guangxi Province. Glacial maxima sea level recessions facilitated connections of different river systems, allowing those from the independent coastal drainages in western Guangdong Province to remain closely related to those from the Pearl River system. Our AMOVA is consistent with the small variation within a clade revealed by the NJ analysis. Speciation within L disparis and phylogenetic positions among clades require further study.
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