关键词: 岩羊, 细胞色素b , 系统起源

Abstract: The blue sheep ( Pseudois nayaur) is a species currently listed as Endangered by IUCN and is registered in the state key protected wildlife list as a Category Ⅱspecies. It is widely distributed in most areas of Southwestern and Northwestern China. There has been no previous molecular examination of the phylogenetic origin of the blue sheep and our research results provide the first preliminary information and molecular perspectives on this problem. mtDNA Cyt b gene was used as genetic marker. Total DNA from three dried skin samples of bharal from Sichuan and Qinghai province in China were extracted and sequenced , and deposited in GenBank ( accession number : AF473606 , AF473607 , AF473608). These complete cyt b gene sequences (1 140 bp) , together with those sequences from goat ( Capra hircus) , ibex ( Capra ibex) , sheep ( Ovis aries) and argali ( Ovis ammon) in the family Bovidae which were obtained from GenBank , were aligned with the MegAlign software. By pairwise comparison , their Kimura 2-parameter distances and base substitutions were analyzed with MEGA software and the percentage differences among them were calculated with Dnastar software. According to two Cyt b molecular clocks , the time when different species began to evolve divergently was estimated. The phylogenetic trees constructed by two methods ( NJ and MP) supported almost the same topology.
Our molecular results showed that the mean sequence difference between blue sheep and the genus Capra (9.67 %) is significantly lower than that between blue sheep and the genus Ovis (11.78 %) . Sequence comparisons showed that the blue sheep is similar to the genus Capra. The phylogenetic analysis revealed that the blue sheep is more closely related to the monophylogeny of the genus Capra than to that of the genus Ovis. The approximate divergent time between bharal and the genus Capra is 3 - 6 Myr , whereas that between bharal and the genus Ovis is 6 - 8 Myr. The primitive-type karyotype is similarly maintained in Capra. A similar chromosomal complement of 2n = 60 is shared by the ibex and the goat. The diploid numbers of the chromosomes of the genus Ovis are 52 , 54 , 56 , 58 and that of blue sheep is 56. Therefore , we propose that blue sheep originated 3 - 6 million years ago when it split up from the genus Capra and developed separately. Further researches are needed in the future by being combined with the fossil records , the characteristics of morphology , behavior biology , and cytogenetics.

Key words: Blue sheep ( Pseudois nayaur), Cytochrome b, Phylogeny