Genetic Divergence Of 4 Structural Genes In Bovinae Livestock Populations

Different taxonomic systems in Bovinae in China have long coexisted in explaining the divergence of Bovinae species. The key problem that affected the evaluation, protection and utilization of genetic resources in Bovinae livestock was the decision of each genus. One opinion prones to classify domestic animals in Bovinae into 6 genuses, Bos, Poephagus, Bison, Bibos, Bubalus and Syncerina. The genus Bos includes species normal cattle (Bos taurus) and zebu (Bos indicus); The genus Poephagus contains only yak (Poephagus grunniens); The genus Bibos includes species gayal(Bibos frontalis), banteng (Bibos javanicus) and India gayal(Bibos gaurus). The genus Bison includes species American bison (Bison bison) and European bison (Bison bonasus). The genus Bubalus includes species Asiatic water buffalo (Bubalus bulalus), tamaraw(Bubalus mindorensis)and the lowland anoa(Bubalus depressicornis), and sometimes the mountain anoa(Bubalus quarlesi), Asiatic water buffalo contains two types, swamp and river type. The genus Syncerina includes species Syncerus caffer and Syncerus nanus. Another opinion proposes that the genuses Poephagus and Bibos be combined into the Bos genus. Moreover, many scholars have different viewpoints on the origins and divergences of some Bovinae species. Chinese water buffalo breeds are generally regarded as swamp type, while some scholars suggested two subbranches in swamp-type water buffalo in China, and others demonstrated that swamp- and river-type water buffaloes independently evoluted and domesticated in China and Indian subcontinentant, and spread to southeast Asia;It is generally thought that Leiqiong cattle originates from Indian zebu (Bos indicus), while some scholars suggested another probable ancient humped cattle origin and a mixture of certain Banteng (Bos javanicus) blood, and deduced that Hainan region in China was probably one of the centers for early origination of Bos species; some scholars suggested that Chinese yak has two subbranches in maternal kinship; to name a few. These different opinions reflect a partial understanding of the issue on the origination and divergence in Bovinae, which leads to a lack of correct theoretical guide for protection of Bovinae genetic resources and an obstacle for effective execution of protection. To collect the information of genetic variations in domestical animals in Bovinae and explore the issue of their evolution and classification, we conducted this research. In the research, by applying simple random sampling in typical colony methods in the central area of habitat, blood samples of 6 typical bovinae species, Mongolia cattle (MG, Bos taurus), Leiqiong cattle (LQ, Bos indicus), Bayingolin yak (MN, Bos grunniens), Dulong gayal (DL, Bos frontalis) , Haizi water buffalo(HZ, Swamp Bubalus bubalis) , Nili-Ravi water buffalo (NR, River Bubalus bubalis), were collected. The genome DNA templates were then extracted from these samples by the regular method in literature. Using the methods of PCR amplification and sequencing, sequences of 4 structural genes, MSTN, GH, ADH and Cyt b, were detected in these 6 populations, and variations of base composition and nucleotides were analyzed by DnaSP and MEGA3.1 softwares, based on which, interpopulational gene flow was analyzed and phylogenic relations among Bovinae were reconstructed to explore the genetic divergence and phylogeny of Bovinae species. The results showed that:1. For the base composition of each gene, G content of Cyt b gene was far (8.3%-13.6%) lower than any of the other three genes; the G+C content of GH gene was about 60%, which was far higher than any of the other three genes; the nucleotide diversities of the three nuclear genes were relatively low among the 6 bovine populations, showing a low genetic diversity;The gene diversities of Cyt b gene were uneven among the 6 bovine populations, highest in Dulong gayal population(0.03807), lowest in Mongolia and Leiqiong cattle populations (0-0.00019), indicating both Mongolia and Leiqiong cattle had relatively a single maternal kinship. For the gene diversities of the 4 genes, Cyt b gene had a highest diversity, the gene diversities of the three nuclear genes were relatively low. These findings were identical with the general knowledge of the evolutionary rate of nuclear and mitochondrial genes.2. The gene diversities between the Bubalus populations and the traditional Bos populations were commonly high, with a low or no gene flow. An exception was that a moderate gene diversity and a faint gene flow were observed. The overall results were in agreement with the traditional taxonomic positions of Bubalus and Bos; Mongolia cattle had not been affected by other maternal kinship; Only in Cyt b gene, a high gene flow level was observed between Dulong gayal and Leiqiong cattle population; a high gene flow level was observed in MSTN gene between Dulong gayal and Bayingolin yak population; a moderate gene diversity and a faint gene flow were observed between the traditional Bos populations and Bayingolin yak population; the gene flow had different effect on these 4 genes, MSTN gene probably insensitive to the pressure of gene flow.3. the yak population was maternally grouped into two subbranches, wild yak and domestic yak; yak was more closely related with American bison than European bison, while the traditional Bos populations were more closely related with European bison than the Bubalus populations or other bovinae populations; the single maternal kinship of the zebu population would not support the supposition of Leiqiong cattle population containing blood of Banteng cattle or Bali cattle, but supported the close relationship between Leiqiong cattle and Indian zebu; Dulong gayal population had maternally close relationships with normal cattle and zebu cattle; the results of two subbranches in Haizi water buffalo population supported the supposition of dividing swamp-type water buffalo into two subbranches, and meanwhile, supported the supposition of its independent domestication; the closer relationship between Haizi water buffalo and tamaraw(Bubalus mindorensis)than the lowland anoa(Bubalus depressicornis)supported partially the supposition of swamp-type water buffalo spreading through two different routes to Southeast Asia.4. on the basis of interpopulational differences at separating sites of genes with moderate evolutionary rate, PCR technique could be used to identify products from diffent bovinae populations, with no special requirements for target gene loci. The overall findings aquired the genetic diversity of these target populations, providing important information for a further understanding of interspecies divergence and partial genetic evidence for the protection and utilization of genetic resources in Bovinae livestock; meanwhile, the study explored the genetic divergence of these 6 target Bovinae populations and species with near relationships, providing objective genetic data for overall researches on the origination and evolution of Bovinae livestocks.