title: The impacts of polyploidy, geographic and ecological isolations on the diversification of Panax (Araliaceae).
abstract: BACKGROUND
  Panax L. is a medicinally important genus within family Araliaceae, where almost all species are of cultural significance for traditional Chinese medicine. Previous studies suggested two independent origins of the East Asia and North America disjunct distribution of this genus and multiple rounds of whole genome duplications (WGDs) might have occurred during the evolutionary process.
  
  
  RESULTS
  We employed multiple chloroplast and nuclear markers to investigate the evolution and diversification of Panax. Our phylogenetic analyses confirmed previous observations of the independent origins of disjunct distribution and both ancient and recent WGDs have occurred within Panax. The estimations of divergence time implied that the ancient WGD might have occurred before the establishment of Panax. Thereafter, at least two independent recent WGD events have occurred within Panax, one of which has led to the formation of three geographically isolated tetraploid species P. ginseng, P. japonicus and P. quinquefolius. Population genetic analyses showed that the diploid species P. notoginseng harbored significantly lower nucleotide diversity than those of the two tetraploid species P. ginseng and P. quinquefolius and the three species showed distinct nucleotide variation patterns at exon regions.
  
  
  CONCLUSIONS
  Our findings based on the phylogenetic and population genetic analyses, coupled with the species distribution patterns of Panax, suggested that the two rounds of WGD along with the geographic and ecological isolations might have together contributed to the evolution and diversification of this genus.
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, 130024, China. shifx816@nenu.edu.cn.
authors.forename: Feng-Xue
authors.initials: FX
authors.lastname: Shi
authors.affiliation: Institute of Grassland Science, Northeast Normal University, Key Laboratory of Vegetation Ecology, Ministry of Education, Changchun, 130024, China. limr145@nenu.edu.cn.
authors.forename: Ming-Rui
authors.initials: MR
authors.lastname: Li
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, 130024, China. liyl378@nenu.edu.cn.
authors.forename: Ya-Ling
authors.initials: YL
authors.lastname: Li
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, 130024, China. jiangp446@nenu.edu.cn.
authors.forename: Peng
authors.initials: P
authors.lastname: Jiang
authors.affiliation: Institute of Grassland Science, Northeast Normal University, Key Laboratory of Vegetation Ecology, Ministry of Education, Changchun, 130024, China. zhangc034@nenu.edu.cn.
authors.forename: Cui
authors.initials: C
authors.lastname: Zhang
authors.affiliation: Kunming Institute of Botany, Chinese Academy of Sciences, Kunming, 650201, China. panyuezhi@mail.kib.ac.cn.
authors.forename: Yue-Zhi
authors.initials: YZ
authors.lastname: Pan
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, 130024, China. baoliu@nenu.edu.cn.
authors.forename: Bao
authors.initials: B
authors.lastname: Liu
authors.affiliation: Institute of Grassland Science, Northeast Normal University, Key Laboratory of Vegetation Ecology, Ministry of Education, Changchun, 130024, China. xiaohx771@nenu.edu.cn.
authors.forename: Hong-Xing
authors.initials: HX
authors.lastname: Xiao
authors.affiliation: Key Laboratory of Molecular Epigenetics of the Ministry of Education (MOE), Northeast Normal University, Changchun, 130024, China. lilf241@nenu.edu.cn.
authors.forename: Lin-Feng
authors.initials: LF
authors.lastname: Li
mesh_terms: D017753:Ecosystem; D019143:Evolution, Molecular; D020440:Gene Duplication; D054628:Genome, Chloroplast; D008969:Molecular Sequence Data; D005894:Panax / Q000235:genetics*; D010802:Phylogeny; D063148:Plant Dispersal; D011123:Polyploidy; D017422:Sequence Analysis, DNA