George M, Ryder O A
Research Department, Zoological Society of San Diego, California 92112.
Mol Biol Evol. 1986 Nov;3(6):535-46. doi: 10.1093/oxfordjournals.molbev.a040414.
Employing mitochondrial DNA (mtDNA) restriction-endonuclease maps as the basis of comparison, we have investigated the evolutionary affinities of the seven species generally recognized as the genus Equus. Individual species' cleavage maps contained an average of 60 cleavage sites for 16 enzymes, of which 29 were invariant for all species. Based on an average divergence rate of 2%/Myr, the variation between species supports a divergence of extant lineages from a common ancestor approximately 3.9 Myr before the present. Comparisons of cleavage maps between Equus przewalskii (Mongolian wild horse) and E. caballus (domestic horse) yielded estimates of nucleotide sequence divergence ranging from 0.27% to 0.41%. This range was due to intraspecific variation, which was noted only for E. caballus. For pairwise comparisons within this family, estimates of sequence divergence ranged from 0% (E. hemionus onager vs. E. h. kulan) to 7.8% (E. przewalskii vs. E. h. onager). Trees constructed according to the parsimony principle, on the basis of 31 phylogenetically informative restriction sites, indicate that the three extant zebra species represent a monophyletic group with E. grevyi and E. burchelli antiquorum diverging most recently. The phylogenetic relationships of E. africanus and E. hemionus remain enigmatic on the basis of the mtDNA analysis, although a recent divergence is unsupported.
以线粒体DNA（mtDNA）限制性内切酶图谱作为比较基础，我们研究了通常被视为马属的七个物种的进化亲缘关系。单个物种的切割图谱平均包含16种酶的60个切割位点，其中29个位点在所有物种中都是不变的。基于平均2%/百万年的分歧率，物种间的差异支持现存谱系自共同祖先在距今约390万年前开始分化。普氏野马（蒙古野马）和家马之间的切割图谱比较得出核苷酸序列分歧估计值在0.27%至0.41%之间。这个范围是由于种内变异造成的，这种变异仅在家马中被观察到。对于该科内的成对比较，序列分歧估计值范围从0%（藏野驴指名亚种与藏野驴昆仑亚种）到7.8%（普氏野马与藏野驴指名亚种）。根据简约原则，基于31个系统发育信息丰富的限制性位点构建的树状图表明，现存的三种斑马物种代表一个单系类群，其中细纹斑马和布氏斑马指名亚种的分化时间最近。基于线粒体DNA分析，非洲野驴和藏野驴的系统发育关系仍然不明，尽管最近的分化缺乏支持。
