title: High levels of effective long-distance dispersal may blur ecotypic divergence in a rare terrestrial orchid.
abstract: BACKGROUND
  Gene flow and adaptive divergence are key aspects of metapopulation dynamics and ecological speciation. Long-distance dispersal is hard to detect and few studies estimate dispersal in combination with adaptive divergence. The aim of this study was to investigate effective long-distance dispersal and adaptive divergence in the fen orchid (Liparis loeselii (L.) Rich.). We used amplified fragment length polymorphism (AFLP)-based assignment tests to quantify effective long-distance dispersal at two different regions in Northwest Europe. In addition, genomic divergence between fen orchid populations occupying two distinguishable habitats, wet dune slacks and alkaline fens, was investigated by a genome scan approach at different spatial scales (continental, landscape and regional) and based on 451 AFLP loci.
  
  
  RESULTS
  We expected that different habitats would contribute to strong divergence and restricted gene flow resulting in isolation-by-adaptation. Instead, we found remarkably high levels of effective long-distance seed dispersal and low levels of adaptive divergence. At least 15% of the assigned individuals likely originated from among-population dispersal events with dispersal distances up to 220 km. Six (1.3%) 'outlier' loci, potentially reflecting local adaptation to habitat-type, were identified with high statistical support. Of these, only one (0.22%) was a replicated outlier in multiple independent dune-fen population comparisons and thus possibly reflecting truly parallel divergence. Signals of adaptation in response to habitat type were most evident at the scale of individual populations.
  
  
  CONCLUSIONS
  The findings of this study suggest that the homogenizing effect of effective long-distance seed dispersal may overwhelm divergent selection associated to habitat type in fen orchids in Northwest Europe.
authors.affiliation: Research Institute for Nature and Forest (INBO), Gaverstraat 4, Geraardsbergen B-9500, Belgium. An.vandenbroeck@inbo.be.
authors.forename: An
authors.initials: A
authors.lastname: Vanden Broeck
authors.forename: Wouter
authors.initials: W
authors.lastname: Van Landuyt
authors.forename: Karen
authors.initials: K
authors.lastname: Cox
authors.forename: Luc
authors.initials: L
authors.lastname: De Bruyn
authors.forename: Ralf
authors.initials: R
authors.lastname: Gyselings
authors.forename: Gerard
authors.initials: G
authors.lastname: Oostermeijer
authors.forename: Bertille
authors.initials: B
authors.lastname: Valentin
authors.forename: Gregor
authors.initials: G
authors.lastname: Bozic
authors.forename: Branko
authors.initials: B
authors.lastname: Dolinar
authors.forename: Zoltán
authors.initials: Z
authors.lastname: Illyés
authors.forename: Joachim
authors.initials: J
authors.lastname: Mergeay
mesh_terms: D000222:Adaptation, Physiological / Q000235:genetics; D054458:Amplified Fragment Length Polymorphism Analysis; D001499:Bayes Theorem; D018744:DNA, Plant / Q000235:genetics; D060146:Ecotype; D005060:Europe; D051456:Gene Flow; D014644:Genetic Variation; D016013:Likelihood Functions; D029595:Orchidaceae / Q000235:genetics*; D058614:Seed Dispersal; D062206:Spatial Analysis
chemical_list: D018744:DNA, Plant