title: Genomic admixture analysis in European Populus spp. reveals unexpected patterns of reproductive isolation and mating.
abstract: Admixture between genetically divergent populations facilitates genomic studies of the mechanisms involved in adaptation, reproductive isolation, and speciation, including mapping of the loci involved in these phenomena. Little is known about how pre- and postzygotic barriers will affect the prospects of "admixture mapping" in wild species. We have studied 93 mapped genetic markers (microsatellites, indels, and sequence polymorphisms, ∼60,000 data points) to address this topic in hybrid zones of Populus alba and P. tremula, two widespread, ecologically important forest trees. Using genotype and linkage information and recently developed analytical tools we show that (1) reproductive isolation between these species is much stronger than previously assumed but this cannot prevent the introgression of neutral or advantageous alleles, (2) unexpected genotypic gaps exist between recombinant hybrids and their parental taxa, (3) these conspicuous genotypic patterns are due to assortative mating and strong postzygotic barriers, rather than recent population history. We discuss possible evolutionary trajectories of hybrid lineages between these species and outline strategies for admixture mapping in hybrid zones between highly divergent populations. Datasets such as this one are still rare in studies of natural hybrid zones but should soon become more common as high throughput genotyping and resequencing become feasible in nonmodel species.
authors.affiliation: University of Wyoming, Department of Botany, Laramie, WY 82071, USA. christian.lexer@unifr.ch
authors.forename: Christian
authors.initials: C
authors.lastname: Lexer
authors.forename: Jeffrey A
authors.initials: JA
authors.lastname: Joseph
authors.forename: Marcela
authors.initials: M
authors.lastname: van Loo
authors.forename: Thelma
authors.initials: T
authors.lastname: Barbará
authors.forename: Berthold
authors.initials: B
authors.lastname: Heinze
authors.forename: Denes
authors.initials: D
authors.lastname: Bartha
authors.forename: Stefano
authors.initials: S
authors.lastname: Castiglione
authors.forename: Michael F
authors.initials: MF
authors.lastname: Fay
authors.forename: C Alex
authors.initials: CA
authors.lastname: Buerkle
mesh_terms: D000220:Adaptation, Biological / Q000235:genetics*; D000483:Alleles; D001483:Base Sequence; D001499:Bayes Theorem; D005075:Biological Evolution; D002874:Chromosome Mapping; D003433:Crosses, Genetic; D003627:Data Interpretation, Statistical; D004843:Epistasis, Genetic; D040961:Genetic Drift; D008040:Genetic Linkage; D005819:Genetic Markers; D049810:Genetic Speciation; D014644:Genetic Variation; D005838:Genotype; D006824:Hybridization, Genetic; D011110:Polymorphism, Genetic; D032107:Populus / Q000235:genetics* / Q000502:physiology*; D012098:Reproduction / Q000235:genetics; D017422:Sequence Analysis, DNA
chemical_list: D005819:Genetic Markers