title: Flow cytometry confirms reticulate evolution and reveals triploidy in Central European Diphasiastrum taxa (Lycopodiaceae, Lycophyta).
abstract: OBJECTIVE
  Interspecific Diphasiastrum hybrids have been assumed to be homoploid and to produce well-formed spores serving sexual reproduction. If this were the case, forms intermediate between hybrids and parents or hybrid swarms should be expected. The purpose of this study was: (1) to check whether homoploidy consistently applies to the three hybrids throughout their Central European range; (2) to examine whether their genome sizes confirm their parentage as assumed by morphology; and (3) to perform a screening for detection of ploidy levels other than diploid and variation in DNA content due to backcrossing.
  
  
  METHODS
  Flow cytometry was used first to measure the relative DNA values [with 4',6-diamidino-2-phenylindole (DAPI) staining] and ploidy level as a general screening, and secondly to determine the absolute DNA 2C values [with propidium iodide (PI) staining] in a number of selected samples with the main focus on the hybrids.
  
  
  RESULTS
  A considerable variation of DNA 2C values (5·26-7·52 pg) was detected between the three European Diphasiastrum species. The values of the diploid hybrids are highly constant without significant variation between regions. They are also intermediate between their assumed parents and agree closely with those calculated from their putative parents. This confirms their hybrid origin, assumed parentage and homoploid status. Considerably higher DNA amounts (9·48-10·30 pg) were obtained for three populations, suggesting that these represent triploid hybrids, an interpretation that is strongly supported by their morphology.
  
  
  CONCLUSIONS
  Diploid hybrids have retained their genetic and morphological identites throughout their Central European range, and thus no indications for diploid backcrossing were found. The triploid hybrids have probably originated from backcrossing between a diploid gametophyte of a hybrid (derived from a diplospore) and a haploid gametophyte of a diploid parental species. By repeated crossing events, reticulate evolution patterns arise that are similar to those known for a number of ferns.
authors.affiliation: Lehrstuhl für Evolution und Biodiversität der Pflanzen, Ruhr-Universität Bochum, Bochum, Germany. wilfried.bennert@rub.de
authors.forename: H Wilfried
authors.initials: HW
authors.lastname: Bennert
authors.forename: Karsten
authors.initials: K
authors.lastname: Horn
authors.forename: Marion
authors.initials: M
authors.lastname: Kauth
authors.forename: Jörg
authors.initials: J
authors.lastname: Fuchs
authors.forename: Iben Sophie Bisgaard
authors.initials: IS
authors.lastname: Jakobsen
authors.forename: Benjamin
authors.initials: B
authors.lastname: Ollgaard
authors.forename: Martin
authors.initials: M
authors.lastname: Schnittler
authors.forename: Matthias
authors.initials: M
authors.lastname: Steinberg
authors.forename: Ronnie
authors.initials: R
authors.lastname: Viane
mesh_terms: D005075:Biological Evolution; D002678:Chimera; D032461:Chromosomes, Plant; D018744:DNA, Plant / Q000032:analysis / Q000235:genetics; D004171:Diploidy; D005060:Europe; D005434:Flow Cytometry; D014644:Genetic Variation; D005843:Geography; D006824:Hybridization, Genetic; D029542:Lycopodiaceae / Q000033:anatomy & histology / Q000235:genetics*; D013045:Species Specificity; D057885:Triploidy
chemical_list: D018744:DNA, Plant