title: Phylogeography of postglacial range expansion in Juglans mandshurica (Juglandaceae) reveals no evidence of bottleneck, loss of genetic diversity, or isolation by distance in the leading-edge populations.
abstract: The past studies of postglacial recolonization patterns in high latitude regions have revealed a significant role of dispersal capacity in shaping the genetic diversity and population structure of temperate trees. However, most of these studies have focused on species with long-distance dispersal followed by exponential population growth and were therefore unable to reveal the patterns in the case of a gradual expansion. Here we studied the impacts of postglacial range expansions on the distribution of genetic diversity in the Manchurian walnut (Juglans mandshurica), a common tree of East Asian cool-temperate deciduous forests that apparently lacks long-distance seed dispersal ability. The genetic diversity and structure of 19 natural walnut populations in Northeast China and the Korean Peninsula were examined using 17 nuclear simple sequence repeat (SSR) loci. Potential habitats under current and past climatic conditions were predicted using the ecological niche modelling (ENM) method. Bayesian clustering analysis revealed three groups, which were inferred to have diverged through multiple glacial-interglacial cycles in multiple refugia during the Quaternary Period. ENM estimated a southward range shift at the LGM, but high suitability scores still occurred in the western parts of the Changbai Mountains (Northeast China), the Korean peninsula and the exposed seafloor of the Yellow Sea. In contrast to most other cool-temperate trees co-occurring in the same region, the Manchurian walnut did not show any evidence of a population bottleneck, loss of genetic diversity or isolation by distance during the postglacial expansion. Our study clearly indicates that current northern populations originated from one glacial lineage and recolonization via a gradually advancing front due to the lack of a long-distance seed dispersal mechanism led to no latitudinal decrease in genetic diversity.
authors.affiliation: MOE Key Laboratory for Biodiversity Science and Ecological Engineering, Beijing Normal University, Beijing 100875, China; School of Mathematics and Computer Science, Northwest University for Nationalities, Lanzhou 730030, China.
authors.forename: Wen-Ting
authors.initials: WT
authors.lastname: Wang
authors.affiliation: MOE Key Laboratory for Biodiversity Science and Ecological Engineering, Beijing Normal University, Beijing 100875, China.
authors.forename: Bing
authors.initials: B
authors.lastname: Xu
authors.affiliation: MOE Key Laboratory for Biodiversity Science and Ecological Engineering, Beijing Normal University, Beijing 100875, China.
authors.forename: Da-Yong
authors.initials: DY
authors.lastname: Zhang
authors.affiliation: MOE Key Laboratory for Biodiversity Science and Ecological Engineering, Beijing Normal University, Beijing 100875, China. Electronic address: baiwn@bnu.edu.cn.
authors.forename: Wei-Ning
authors.initials: WN
authors.lastname: Bai
mesh_terms: D001499:Bayes Theorem; D002467:Cell Nucleus / Q000235:genetics; D002736:Chloroplasts / Q000235:genetics; D018744:DNA, Plant / Q000737:chemistry / Q000302:isolation & purification / Q000378:metabolism; D017753:Ecosystem; D014644:Genetic Variation; D005828:Genetics, Population; D005838:Genotype; D031324:Juglans / Q000145:classification* / Q000235:genetics; D018895:Microsatellite Repeats / Q000235:genetics; D010802:Phylogeny; D058974:Phylogeography
chemical_list: D018744:DNA, Plant
keywords: Cool-temperate forest; East Asia; Microsatellite variation; Northern refugia; Quaternary glaciations