关键词: 线粒体DNA, 限制性片断长度多态性, 藏鼠兔及高原鼠兔

Abstract: The two species，Ochotona thibetana and O.cutzoniae(genus Ochotona)，are easily
distinguishable based on traditional morphological characteristics. But what about the characteristics ata molecrlar level? We know little about them.So the analysis of genetic differences between the two species at DNA level may provide useful data for systematics and evolutionary biology. Besides morphological comparison，patterns of mitochondrial DNA (mtDAN )variation were evaluated between the two species．In this study,purified mtDNA was digested with 16 restriction endonucleases that recognized 6-bp sequences．Lambda DNA fragments disgested with Hind Ⅲ were used as molecular weight standards．The molecular size of mtDNA from two species was about 17.9kb．A total of 30 restriction types were recognized by the sixteen enzymes．Of these enzymes，twelve display interspecific site polymorphism．Therefore，extensive site polymorphism exists between the two species．The average number of nucleotide substitutions per site(genetic distance)between them is 0.0455．If the base substitution rate of pikas mtDNA was 2% per million years，then the divergency of the two species would have happened about 2.3 Myr ago (Late Pliocene or Yushea/early Nihewangian of the Chinese mammalian age)．This calculation appears to be substantiated by the fossil record．

Key words: Mitochondrial DNA, Restriction fragment length polymorphism(RFLP), Moupin Pika and Black-lipped or Plateau Pika