title: Multiple hybridization events in Cardamine (Brassicaceae) during the last 150 years: revisiting a textbook example of neoallopolyploidy.
abstract: OBJECTIVE
  Recently formed allopolyploid species represent excellent subjects for exploring early stages of polyploid evolution. The hexaploid Cardamine schulzii was regarded as one of the few nascent allopolyploid species formed within the past ∼150 years that presumably arose by autopolyploidization of a triploid hybrid, C. × insueta; however, the most recent investigations have shown that it is a trigenomic hybrid. The aims of this study were to explore the efficiency of progenitor-specific microsatellite markers in detecting the hybrid origins and genome composition of these two allopolyploids, to estimate the frequency of polyploid formation events, and to outline their evolutionary potential for long-term persistence and speciation.
  
  
  METHODS
  Flow-cytometric ploidy-level screening and genotyping by progenitor-specific microsatellite markers (20 microsatellite loci) were carried out on samples focused on hybridizing populations at Urnerboden, Switzerland, but also including comparative material of the parental species from other sites in the Alps and more distant areas.
  
  
  RESULTS
  It was confirmed that hybridization between the diploids C. amara and C. rivularis auct. gave rise to triploid C. × insueta, and it is inferred that this has occurred repeatedly. Evidence is provided that C. schulzii comprises three parental genomes and supports its origin from hybridization events between C. × insueta and the locally co-occurring hypotetraploid C. pratensis, leading to two cytotypes of C. schulzii: hypopentaploid and hypohexaploid. Each cytotype of C. schulzii is genetically uniform, suggesting their single origins.
  
  
  CONCLUSIONS
  Persistence of C. schulzii has presumably been achieved only by perennial growth and clonal reproduction. This contrasts with C. × insueta, in which multiple origins and occasional sexual reproduction have generated sufficient genetic variation for long-term survival and evolutionary success. This study illustrates a complex case of recurrent hybridization and polyploidization events, and highlights the role of triploids that promoted the origin of trigenomic hybrids.
authors.affiliation: Institute of Botany, Slovak Academy of Sciences, Dúbravská cesta 9, SK-845 23 Bratislava, Slovak Republic.
authors.forename: Judita
authors.initials: J
authors.lastname: Zozomová-Lihová
authors.forename: Karol
authors.initials: K
authors.lastname: Krak
authors.forename: Terezie
authors.initials: T
authors.lastname: Mandáková
authors.forename: Kentaro K
authors.initials: KK
authors.lastname: Shimizu
authors.forename: Stanislav
authors.initials: S
authors.lastname: Spaniel
authors.forename: Petr
authors.initials: P
authors.lastname: Vít
authors.forename: Martin A
authors.initials: MA
authors.lastname: Lysak
mesh_terms: D005075:Biological Evolution; D031217:Cardamine / Q000235:genetics*; D018744:DNA, Plant; D005434:Flow Cytometry; D005819:Genetic Markers; D006824:Hybridization, Genetic; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D010802:Phylogeny; D011123:Polyploidy; D017422:Sequence Analysis, DNA; D013557:Switzerland
chemical_list: D018744:DNA, Plant; D005819:Genetic Markers
keywords: Allopolyploidy; Alps; Brassicaceae; Cardamine schulzii; Cardamine × insueta; hybridization; microsatellites; neoallopolyploidy; polyploid evolution; speciation