title: Patterns of hybridization between diploid and derived allotetraploid species of Dactylorhiza (Orchidaceae) co-occurring in Belgium.
abstract: OBJECTIVE
  Although the potential for gene flow between species with large differences in chromosome numbers has long been recognized, only few studies have thoroughly investigated in situ hybridization across taxa with different ploidy levels. We combined morphological, cytological, and genetic marker data with pollination experiments to investigate the degree, direction, and spatial pattern of hybridization between the diploid Dactylorhiza incarnata and its tetraploid derivative, D. praetermissa.
  
  
  METHODS
  To identify hybrids, 169 individuals were genotyped using AFLPs and morphologically characterized. Individuals were clustered on the basis of their AFLP profile using the program Structure. To reduce the dimensionality of the plant-trait matrix, PCA was applied. The origin of suspected hybrid individuals was verified using flow cytometry. An AMOVA and spatial autocorrelation analysis were used to indirectly infer the extent of gene flow.
  
  
  RESULTS
  Only five individuals were regarded as putative hybrids on the basis of the AFLP data; all had been assigned to the D. praetermissa morphotype. Only one had deviating DNA content and was presumably a triploid. High Φ(ST) values between different subpopulations and significant spatial genetic structure were observed, suggesting localized gene flow.
  
  
  CONCLUSIONS
  Using combined data to study hybridization between D. incarnata and D. praetermissa, very few unequivocal hybrids were observed. We propose several non-mutually exclusive explanations. Localized pollen flow, in combination with different microhabitat preferences, is probably one of the reasons for the low frequency of hybrids. Also, the triploid first-generation hybrids may experience difficulties in successful establishment, as a result of genic incompatibilities.
authors.affiliation: Biology Department, Laboratory of Plant Ecology, University of Leuven, Kasteelpark Arenberg 31, B-3001 Heverlee, Belgium. koen.dehert@bio.kuleuven.be
authors.forename: Koen
authors.initials: K
authors.lastname: De Hert
authors.forename: Hans
authors.initials: H
authors.lastname: Jacquemyn
authors.forename: Sabine
authors.initials: S
authors.lastname: Van Glabeke
authors.forename: Isabel
authors.initials: I
authors.lastname: Roldán-Ruiz
authors.forename: Katrien
authors.initials: K
authors.lastname: Vandepitte
authors.forename: Leen
authors.initials: L
authors.lastname: Leus
authors.forename: Olivier
authors.initials: O
authors.lastname: Honnay
mesh_terms: D054458:Amplified Fragment Length Polymorphism Analysis; D001530:Belgium; D016000:Cluster Analysis; D004171:Diploidy; D035264:Flowers / Q000502:physiology; D005638:Fruit / Q000502:physiology; D014644:Genetic Variation; D006824:Hybridization, Genetic; D029595:Orchidaceae / Q000033:anatomy & histology / Q000235:genetics* / Q000502:physiology; D054817:Pollination / Q000502:physiology; D025341:Principal Component Analysis; D012098:Reproduction / Q000235:genetics; D012621:Seasons; D012639:Seeds / Q000502:physiology; D013045:Species Specificity; D057891:Tetraploidy