title: Genetic origin and composition of a natural hybrid poplar Populus × jrtyschensis from two distantly related species.
abstract: BACKGROUND
  The factors that contribute to and maintain hybrid zones between distinct species are highly variable, depending on hybrid origins, frequencies and fitness. In this study, we aimed to examine genetic origins, compositions and possible maintenance of Populus × jrtyschensis, an assumed natural hybrid between two distantly related species. This hybrid poplar occurs mainly on the floodplains along the river valleys between the overlapping distributions of the two putative parents.
  
  
  RESULTS
  We collected 566 individuals from 45 typical populations of P. × jrtyschensis, P. nigra and P. laurifolia. We genotyped them based on the sequence variations of one maternally inherited chloroplast DNA (cpDNA) fragment and genetic polymorphisms at 20 SSR loci. We further sequenced eight nuclear genes for 168 individuals from 31 populations. Two groups of cpDNA haplotypes characteristic of P. nigra and P. laurifolia respectively were both recovered for P. × jrtyschensis. Genetic structures and coalescent tests of two sets of nuclear population genetic data suggested that P. × jrtyschensis originated from hybridizations between the two assumed parental species. All examined populations of P. × jrtyschensis comprise mainly F1 hybrids from interspecific hybridizations between P. nigra and P. laurifolia. In the habitats of P. × jrtyschensis, there are lower concentrations of soil nitrogen than in the habitats occupied by the other two species.
  
  
  CONCLUSIONS
  Our extensive examination of the genetic composition of P. × jrtyschensis suggested that it is typical of F1-dominated hybrid zones. This finding plus the low concentration of soil nitrogen in the floodplain soils support the F1-dominated bounded hybrid superiority hypothesis of hybrid zone maintenance for this particular hybrid poplar.
authors.affiliation: State Key Laboratory of Grassland Agro-Ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China.
authors.forename: Dechun
authors.initials: D
authors.lastname: Jiang
authors.affiliation: State Key Laboratory of Grassland Agro-Ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China.|College of Plant Sciences, Xinjiang Production & Construction Corps Key Laboratory of Protection and Utilization of Biological Resources in Tarim Basin, Tarimu University, Alar, Xinjiang, People's Republic of China.
authors.forename: Jianju
authors.initials: J
authors.lastname: Feng
authors.affiliation: State Key Laboratory of Grassland Agro-Ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China.
authors.forename: Miao
authors.initials: M
authors.lastname: Dong
authors.affiliation: State Key Laboratory of Grassland Agro-Ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China.
authors.forename: Guili
authors.initials: G
authors.lastname: Wu
authors.affiliation: State Key Laboratory of Grassland Agro-Ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China.
authors.forename: Kangshan
authors.initials: K
authors.lastname: Mao
authors.affiliation: State Key Laboratory of Grassland Agro-Ecosystem, School of Life Sciences, Lanzhou University, Lanzhou, Gansu, People's Republic of China. liujq@lzu.edu.cn.
authors.forename: Jianquan
authors.initials: J
authors.lastname: Liu
mesh_terms: D002467:Cell Nucleus / Q000235:genetics; D018742:DNA, Chloroplast / Q000737:chemistry / Q000235:genetics*; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics; D017753:Ecosystem; D055868:Floods; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D005843:Geography; D006239:Haplotypes; D006823:Hybrid Vigor / Q000235:genetics; D006824:Hybridization, Genetic; D018895:Microsatellite Repeats / Q000235:genetics*; D011110:Polymorphism, Genetic; D032107:Populus / Q000145:classification / Q000235:genetics* / Q000254:growth & development; D045483:Rivers; D017422:Sequence Analysis, DNA; D013045:Species Specificity
chemical_list: D018742:DNA, Chloroplast; D018744:DNA, Plant
keywords: First-generation hybrids; Hybrid origin; Hybrid superiority; Populus × jrtyschensis