Origin and Dispersal of Early Domestic Pigs in Northern China
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www.nature.com/scientificreports OPEN Origin and dispersal of early domestic pigs in northern China Hai Xiang1,2, Jianqiang Gao3, Dawei Cai4, Yunbing Luo5, Baoquan Yu6, Langqing Liu1, Ranran Liu7, Hui Zhou4, Xiaoyong Chen8, Weitao Dun8, Xi Wang9, Michael Hofreiter10 & Xingbo Zhao1 Received: 16 February 2017 It is widely accepted that modern pigs were domesticated independently at least twice, and Chinese Accepted: 7 June 2017 native pigs are deemed as direct descendants of the first domesticated pigs in the corresponding Published: xx xx xxxx domestication centers. By analyzing mitochondrial DNA sequences of an extensive sample set spanning 10,000 years, we find that the earliest pigs from the middle Yellow River region already carried the maternal lineages that are dominant in both younger archaeological populations and modern Chinese pigs. Our data set also supports early Neolithic pig utilization and a long-term in situ origin for northeastern Chinese pigs during 8,000–3,500 BP, suggesting a possibly independent domestication in northeast China. Additionally, we observe a genetic replacement in ancient northeast Chinese pigs since 3,500 BP. The results not only provide increasing evidence for pig origin in the middle Yellow River region but also depict an outline for the process of early pig domestication in northeast China. It is widely accepted that pigs were domesticated independently in Near East and East Asia beginning ~10,000 years ago after Sus sp. emerged in Southeast Asia during the climatic fluctuations of the early Pliocene 5.3–3.5 My ago1–3. So far, at least six phylogeographically distinct wild boar lineages have been found to have contributed to the present domestic pig populations4. Over the past decade, regions in China, including the Mekong River basin5, the downstream region of the Yangtze River5, the upper stream region of the Yangtze River6, the Tibetan highlands7 and the lower region of the Yellow River8, 9 have been suggested as regions from which wild boar have contributed to the domestic pig gene pool and which may have represented independent centers for pig domestication. Zoo-archaeological studies on the pig remains from the Early Neolithic assemblages in China back this idea of multiregional pig domestication in East Asia. The faunal assemblages of the ~9,000-y-old Zhenpiyan cave site10 in Guangxi province and the ~8,000-y-old Kuahuqiao site11 in Zhejiang Province both provide evidence for a commensal domestication phase12 in the Mekong River basin and the downstream region of Yangtze River. Furthermore, numerous pig remains excavated in the ~10,500-y-old Nanzhuangtou site13, the ~9,000-y-old Jiahu site14, and the ~7,500-y-old Cishan site15 as well as palaeogenetic studies8 presented the middle and lower branches of the Yellow River as one of the earliest regions for pig domestication. Extensive archaeological findings in these regions, such as broomcorn millet, foxtail millet, dog and chicken, are evidence for early origins of mixed agriculture16–18. Besides the archaeological findings, pigs seem to have had cultural significance for the commu- nities in this region because two pig skeletons were buried with humans at Xinglongwa Site (8,200–7,400 BP), implying either that pigs may already have been domesticated in Northeast China around 8,000 years ago or that wild boar had cultural significance19, 20. It has previously been shown that, at least with regard to maternal lineages, Chinese native pig breeds were direct descendants of the first domesticated pigs in the corresponding geographical regions8, 9. However, it is 1National Engineering Laboratory for Animal Breeding; Ministry of Agricultural Key Laboratory of Animal Genetics, Breeding and Reproduction; and College of Animal Science and Technology, China Agricultural University, Beijing, 100193, China. 2Institute of Genetics and Developmental Biology, Chinese Academy of Sciences, Beijing, 100101, China. 3Hebei Provincial Institute of Cultural Relic, Shijiazhuang, 050031, China. 4Ancient DNA Laboratory, Research Center for Chinese Frontier Archaeology, Jilin University, Changchun, 130023, China. 5Hubei Provincial Institute of Cultural Relics and Archaeology, Wuhan, 430077, China. 6Xushui County Office for Preservation of Ancient Monuments, Xushui, 072550, China. 7Institute of Animal Sciences, Chinese Academy of Agricultural Sciences, Beijing, 100193, China. 8Institute of Animal Science and Veterinary of Hebei Province, Baoding, 071000, China. 9Institute of Animal Science and Veterinary Medicine, Shanxi Academy of Agricultural Science, Taiyuan, 030032, China. 10Faculty of Mathematics and Natural Sciences, Institute for Biochemistry and Biology, University of Potsdam, Karl- Liebknecht-Str. 24-25, Potsdam, 14476, Germany. Correspondence and requests for materials should be addressed to M.H. (email: [email protected]) or X.Z. (email: [email protected]) SCIENTIFIC REPORTS | 7: 5602 | DOI:10.1038/s41598-017-06056-8 1 www.nature.com/scientificreports/ Figure 1. Locations of samples. The orange dots depict all sites from which we retrieved ancient pig sequences. The inset shows the location of the region within China. The maps are modified from free map materials deposited in the public database of National Administration of Surveying, Mapping and Geoinformation (http://219.238.166.215/mcp/index.asp). likely that roaming in a semi-managed status during the beginning of domestication allowed recurrent genetic exchange between domesticated pigs and indigenous wild boars. Thus, even during the beginning of domesti- cation, genetic similarity between domestic pigs and wild boar from the same region may indicate introgression of wild boar haplotypes into the domestic gene pool rather than independent domestication events. Moreover, human migrations and cultural expansions repeatedly took place in East Asia during the past 10,000 years. Thus, human-mediated dispersal of and gene flow among domestic pig populations would not have been uncommon. Both for European and Near Eastern pigs, ancient DNA and dental geometric morphometric analyses have revealed nonlinear patterns of early domestication, dispersal of animals, genetic turnover and interaction among various geographic regions21–23. We have collected pig remains from 15 archaeological sites in China, including Jiahu and another two of the oldest archaeological sites in the middle Yellow River basin (Nanzhuangtou and Cishan), three sites in Northeast China (Xinglongwa, Wanfabozi and Dashanqian), and one site (Changning) in the upper region of the Yellow River. We investigated partial mitochondrial DNA control region (CR) sequences and a segment of the cytochrome b gene (Cytb) from both ancient and modern pigs, aiming to uncover the pattern of early maternal domestication and lineage dispersal in China. Locations and details for all samples can be found in Fig. 1 and Table S1. Results Using loop-mediated PCR (L-PCR) followed by a specific singleplex PCR (for primers used see Table S2), we retrieved 49 Cytb fragments (Table S3) and 15 CR fragments (Table S4) of ancient pig samples from 15 archae- ological sites. By combining our new results with previously reported sequences, we obtained a data set of 38 ancient pig CR sequences from China (Table S4) and combined Cytb/CR sequences from 37 samples, ranging geographically from northeast to northwest China and temporally from 10,000 BP to 2,500 BP (Table S1). We confirmed the Neolithic context of some of the early samples by determining the ages of the archaeological pig bones by direct radiocarbon dating of two bones from Cishan site, one bone from Nanzhuangtou site and one bone from Xinglongwa site. These samples yielded calibrated dates of ∼7,600, ∼7,800, ∼10,500 and ∼7,500 years, respectively (Tables S1 and S5), confirming the archaeologically determined ages. We aligned the 37 combined sequences with 97 published homologous sequences of extant wild boar, native pig breeds and commercial pig breeds from all over the world (Table S6). Phylogenetic analyses resulted in two apparent clusters, which represent Asian and European origins, respectively (Fig. 2). All 10,000 BP to 2,500 BP Chinese pigs were found in the Asian clade (Fig. 2). To investigate the source of the genetic diversity in Asian pigs in more detail, we compared ancient and mod- ern Asian pigs based on the mitochondrial Cytb sequences alone. We aligned our 49 ancient sequences (Table S3) with 506 extant homologous sequences, which represent modern Asian pigs deposited in GenBank (Table S7). We found 20 SNPs among all Asian pig sequences, which constituted 21 haplotypes (Table S7). The 20 SNPs included 10 nonsynonymous substitutions, by which we classified Asian pigs into 11 groups defined by different SCIENTIFIC REPORTS | 7: 5602 | DOI:10.1038/s41598-017-06056-8 2 www.nature.com/scientificreports/ Figure 2. Bayesian consensus phylogenetic tree of the 37 combined (Cytb and control region) ancient pig sequences and 98 extant published homologous sequences. Ages (modern vs. ancient), status (wild vs. domestic) and geographical origin are depicted in different colours (see bottom left of the figure). The European and Asian sequence clusters are framed. Cytb amino acid sequences. The group AA1 contained 10 haplotypes representing 525 sequences (almost 95% of the sequences) and all geographically defined pig types from Asia (Fig. 3a and b), making this haplogroup the predominant haplogroup among Asian pigs. The groups AA2-AA11 contained the remaining 30 sequences, rep- resenting