title: Molecular evidence for convergent evolution and allopolyploid speciation within the Physcomitrium-Physcomitrella species complex.
abstract: BACKGROUND
  The moss Physcomitrella patens (Hedw.) Bruch & Schimp. is an important experimental model system for evolutionary-developmental studies. In order to shed light on the evolutionary history of Physcomitrella and related species within the Funariaceae, we analyzed the natural genetic diversity of the Physcomitrium-Physcomitrella species complex.
  
  
  RESULTS
  Molecular analysis of the nuclear single copy gene BRK1 reveals that three Physcomitrium species feature larger genome sizes than Physcomitrella patens and encode two expressed BRK1 homeologs (polyploidization-derived paralogs), indicating that they may be allopolyploid hybrids. Phylogenetic analyses of BRK1 as well as microsatellite simple sequence repeat (SSR) data confirm a polyphyletic origin for three Physcomitrella lineages. Differences in the conservation of mitochondrial editing sites further support hybridization and cryptic speciation within the Physcomitrium-Physcomitrella species complex.
  
  
  CONCLUSIONS
  We propose a revised classification of the previously described four subspecies of Physcomitrella patens into three distinct species, namely Physcomitrella patens, Physcomitrella readeri and Physcomitrella magdalenae. We argue that secondary reduction of sporophyte complexity in these species is due to the establishment of an ecological niche, namely spores resting in mud and possible spore dispersal by migratory birds. Besides the Physcomitrium-Physcomitrella species complex, the Funariaceae are host to their type species, Funaria hygrometrica, featuring a sporophyte morphology which is more complex. Their considerable developmental variation among closely related lineages and remarkable trait evolution render the Funariaceae an interesting group for evolutionary and genetic research.
authors.forename: Anna K
authors.initials: AK
authors.lastname: Beike
authors.forename: Mark
authors.initials: M
authors.lastname: von Stackelberg
authors.forename: Mareike
authors.initials: M
authors.lastname: Schallenberg-Rüdinger
authors.forename: Sebastian T
authors.initials: ST
authors.lastname: Hanke
authors.forename: Marie
authors.initials: M
authors.lastname: Follo
authors.forename: Dietmar
authors.initials: D
authors.lastname: Quandt
authors.forename: Stuart F
authors.initials: SF
authors.lastname: McDaniel
authors.forename: Ralf
authors.initials: R
authors.lastname: Reski
authors.forename: Benito C
authors.initials: BC
authors.lastname: Tan
authors.affiliation: Faculty of Biology, University of Freiburg, Schänzlestr, 1, 79104 Freiburg, Germany. stefan.rensing@biologie.uni-marburg.de.
authors.forename: Stefan A
authors.initials: SA
authors.lastname: Rensing
mesh_terms: D005075:Biological Evolution; D019068:Bryopsida / Q000145:classification* / Q000235:genetics*; D003001:Cloning, Molecular; D014644:Genetic Variation; D006824:Hybridization, Genetic; D018895:Microsatellite Repeats; D008969:Molecular Sequence Data; D010802:Phylogeny; D011123:Polyploidy; D017422:Sequence Analysis, DNA