title: Biogeographic variation in genetic variability, apomixis expression and ploidy of St. John's wort (Hypericum perforatum) across its native and introduced range.
abstract: OBJECTIVE
  St. John's wort (Hypericum perforatum) is becoming an important model plant system for investigations into ecology, reproductive biology and pharmacology. This study investigates biogeographic variation for population genetic structure and reproduction in its ancestral (European) and introduced (North America) ranges.
  
  
  METHODS
  Over 2000 individuals from 43 localities were analysed for ploidy, microsatellite variation (19 loci) and reproduction (flow cytometric seed screen). Most individuals were tetraploid (93%), while lower frequencies of hexaploid (6%), diploid (<1%) and triploid (<1%) individuals were also identified.
  
  
  RESULTS
  A flow cytometric analysis of 24 single seeds per individual, and five individuals per population demonstrated opposite patterns between ploidy types, with tetraploids producing more apomictic (73%) than sexual (24%) seed, while hexaploids produced more sexual (73%) than apomictic (23%) seed. As hexaploids are derived from tetraploids, these data imply that gene dosage, in addition to the effects of hybridization, influences the switch from apomictic to sexual reproduction. No significant differences in seed production were found between Europe and North America. An analysis of population structure based upon microsatellite profiling demonstrated three major genetic clusters in Europe, whose distribution was reflective of Pleistocene glaciation (e.g. refugia) and post-glacial recolonization of Europe.
  
  
  CONCLUSIONS
  The presence of pure and mixed populations representing all three genetic clusters in North America demonstrates that H. perforatum was introduced multiple times onto the continent, followed by gene flow between the different gene pools. Taken together, the data presented here suggest that plasticity in reproduction has no influence on the invasive potential of H. perforatum.
authors.affiliation: Apomixis research group, Leibniz Institut für Pflanzengenetik und Kulturpflanzenforschung (IPK), Corrensstrasse 3, D-06466 Gatersleben, Germany.
authors.forename: Marta Puente
authors.initials: MP
authors.lastname: Molins
authors.forename: José M
authors.initials: JM
authors.lastname: Corral
authors.forename: Olawale Mashood
authors.initials: OM
authors.lastname: Aliyu
authors.forename: Marcus A
authors.initials: MA
authors.lastname: Koch
authors.forename: Anja
authors.initials: A
authors.lastname: Betzin
authors.forename: John L
authors.initials: JL
authors.lastname: Maron
authors.forename: Timothy F
authors.initials: TF
authors.lastname: Sharbel
mesh_terms: D060832:Apomixis / Q000235:genetics*; D001499:Bayes Theorem; D005060:Europe; D005434:Flow Cytometry; D051456:Gene Flow; D014644:Genetic Variation; D005828:Genetics, Population; D006824:Hybridization, Genetic; D020902:Hypericum / Q000235:genetics* / Q000502:physiology; D058865:Introduced Species; D018895:Microsatellite Repeats / Q000235:genetics; D009656:North America; D058974:Phylogeography; D011003:Ploidies; D012098:Reproduction; D012639:Seeds / Q000235:genetics
keywords: Hypericum perforatum; St John's wort; apomixis; hybridization; invasiveness; polyploidy