title: Multispecies genetic structure and hybridization in the Betula genus across Eurasia.
abstract: Boreal and cool temperate forests are the major land cover of northern Eurasia, and information about continental-scale genetic structure and past demographic history of forest species is important from an evolutionary perspective and has conservation implications. However, although many population genetic studies of forest tree species have been conducted in Europe or Eastern Asia, continental-scale genetic structure and past demographic history remain poorly known. Here, we focus on the birch genus Betula, which is commonly distributed in boreal and cool temperate forests, and examine 129 populations of two tetraploid and four diploid species collected from Iceland to Japan. All individuals were genotyped at seven to 18 nuclear simple sequence repeats (nSSRs). Pairwise FST' among the six species ranged from 0.285 to 0.903, and genetic differentiation among them was clear. structure analysis suggested that Betula pubescens is an allotetraploid and one of the parental species was Betula pendula. In both species pairs of B. pendula and B. plathyphylla, and B. pubescens and B. ermanii, genetic diversity was highest in central Siberia. A hybrid zone was detected around Lake Baikal for eastern and western species pairs regardless of ploidy level. Approximate Bayesian computation suggested that the divergence of B. pendula and B. platyphylla occurred around the beginning of the last ice age (36 300 years BP, 95% CI: 15 330-92 700) and hybridization between them was inferred to have occurred after the last glacial maximum (1614 years BP, 95% CI: 561-4710), with B. pendula providing a higher contribution to hybrids.
authors.affiliation: Department of Ecology and Genetics, Evolutionary Biology Centre, Science for Life Laboratory, Uppsala University, Norbyvägen 18D, 75236, Uppsala, Sweden.|Institute of Biosciences and Bioresources, Division of Florence, National Research Council, Via Madonna del Piano 10, 50019, Sesto Fiorentino (Firenze), Italy.
authors.forename: Yoshiaki
authors.initials: Y
authors.lastname: Tsuda
authors.affiliation: Institute of Plant and Animal Ecology, Ural Branch of Russian Academy of Science, Ekaterinburg, 620144, Russia.
authors.forename: Vladimir
authors.initials: V
authors.lastname: Semerikov
authors.affiliation: Institute of Biosciences and Bioresources, Division of Florence, National Research Council, Via Madonna del Piano 10, 50019, Sesto Fiorentino (Firenze), Italy.
authors.forename: Federico
authors.initials: F
authors.lastname: Sebastiani
authors.affiliation: Institute of Biosciences and Bioresources, Division of Florence, National Research Council, Via Madonna del Piano 10, 50019, Sesto Fiorentino (Firenze), Italy.
authors.forename: Giovanni Giuseppe
authors.initials: GG
authors.lastname: Vendramin
authors.affiliation: Department of Ecology and Genetics, Evolutionary Biology Centre, Science for Life Laboratory, Uppsala University, Norbyvägen 18D, 75236, Uppsala, Sweden.
authors.forename: Martin
authors.initials: M
authors.lastname: Lascoux
mesh_terms: D001499:Bayes Theorem; D029662:Betula / Q000145:classification*; D005060:Europe; D005202:Asia, Eastern; D005828:Genetics, Population; D006824:Hybridization, Genetic; D007055:Iceland; D007564:Japan; D018895:Microsatellite Repeats; D012800:Siberia
keywords: 
  Betula
  ; Eurasia; allotetraploid; demographic history; genetic structure; species delimitation