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Open Access Highly Accessed Research article

Molecular evidence for convergent evolution and allopolyploid speciation within the Physcomitrium-Physcomitrella species complex

Anna K Beike12, Mark von Stackelberg24, Mareike Schallenberg-Rüdinger10, Sebastian T Hanke1103, Marie Follo6, Dietmar Quandt5, Stuart F McDaniel7, Ralf Reski2389, Benito C Tan11 and Stefan A Rensing11039*

Author Affiliations

1 Faculty of Biology, University of Freiburg, Schänzlestr. 1, 79104 Freiburg, Germany

2 Plant Biotechnology, Faculty of Biology, University of Freiburg, Schänzlestr. 1, 79104 Freiburg, Germany

3 FRISYS Freiburg Initiative for Systems Biology, University of Freiburg, 79104 Freiburg, Germany

4 Present address: Käthe-Kollwitz-Schule, Reserveallee 5, 76646 Bruchsal, Germany

5 Nees Institute for Biodiversity of Plants, University of Bonn, Meckenheimer Allee 170, 53115 Bonn, Germany

6 Department of Medicine I, University Medical Center Freiburg, 79106 Freiburg, Germany

7 University of Florida, Gainesville, FL 32611, USA

8 FRIAS Freiburg Institute for Advanced Studies, University of Freiburg, 79104 Freiburg, Germany

9 BIOSS Centre for Biological Signalling Studies, University of Freiburg, 79104 Freiburg, Germany

10 Plant Cell Biology, Faculty of Biology, University of Marburg, Karl-von-Frisch-Str. 8, 35043 Marburg, Germany

11 The University and Jepson Herbaria, University of California, Berkeley, CA 94720, USA

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BMC Evolutionary Biology 2014, 14:158  doi:10.1186/1471-2148-14-158

Published: 11 July 2014

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.

Keywords:
Physcomitrella patens; Funariaceae; Hybridization; Polyploidization; Speciation