title: Retention of gene diversity during the spread of a non-native plant species.
abstract: Spatial expansion, which is a crucial stage in the process to successful biological invasion, is anticipated to profoundly affect the magnitude and spatial distribution of genetic diversity in novel colonized areas. Here, we show that, contrasting common expectations, Pyrenean rocket (Sisymbrium austriacum), retained SNP diversity as this introduced plant species descended in the Meuse River Basin. Allele frequencies did not mirror between-population distances along the predominant expansion axis. Reconstruction of invasion history based on the genotypes of historical herbarium specimens indicated no influence of additional introductions or multiple points of entry on this nongradual pattern. Assignment analysis suggested the admixture of distant upstream sources in recently founded downstream populations. River dynamics seem to have facilitated occasional long-distance dispersal which brought diversity to the expansion front and so maintained evolutionary potential. Our findings highlight the merit of a historical framework in interpreting extant patterns of genetic diversity in introduced species and underscore the need to integrate long-distance dispersal events in theoretical work on the genetic consequences of range expansion.
authors.affiliation: Plant Conservation and Population Biology, Biology Department, University of Leuven, Heverlee, Belgium.
authors.forename: Katrien
authors.identifier: http://orcid.org/0000-0003-1031-8728
authors.initials: K
authors.lastname: Vandepitte
authors.affiliation: Plant Conservation and Population Biology, Biology Department, University of Leuven, Heverlee, Belgium.|Department of Biology, Norwegian University of Science and Technology, Trondheim, Norway.
authors.forename: Kenny
authors.initials: K
authors.lastname: Helsen
authors.affiliation: Plant Conservation and Population Biology, Biology Department, University of Leuven, Heverlee, Belgium.
authors.forename: Kasper
authors.initials: K
authors.lastname: Van Acker
authors.affiliation: Research Institute for Nature and Forest, Geraardsbergen, Belgium.
authors.forename: Joachim
authors.initials: J
authors.lastname: Mergeay
authors.affiliation: Plant Conservation and Population Biology, Biology Department, University of Leuven, Heverlee, Belgium.
authors.forename: Olivier
authors.initials: O
authors.lastname: Honnay
mesh_terms: D005075:Biological Evolution; D019607:Brassicaceae / Q000235:genetics*; D005787:Gene Frequency; D014644:Genetic Variation; D005838:Genotype; D058865:Introduced Species; D063148:Plant Dispersal
keywords: 
  SNP
  ; genic diversity; herbarium specimen; introduction history; non-native plant; population genetic; reconstruction; spatial expansion