title: Multiple ITS copies reveal extensive hybridization within Rheum (Polygonaceae), a genus that has undergone rapid radiation.
abstract: BACKGROUND
  During adaptive radiation events, characters can arise multiple times due to parallel evolution, but transfer of traits through hybridization provides an alternative explanation for the same character appearing in apparently non-sister lineages. The signature of hybridization can be detected in incongruence between phylogenies derived from different markers, or from the presence of two divergent versions of a nuclear marker such as ITS within one individual.
  
  
  RESULTS
  In this study, we cloned and sequenced ITS regions for 30 species of the genus Rheum, and compared them with a cpDNA phylogeny. Seven species contained two divergent copies of ITS that resolved in different clades from one another in each case, indicating hybridization events too recent for concerted evolution to have homogenised the ITS sequences. Hybridization was also indicated in at least two further species via incongruence in their position between ITS and cpDNA phylogenies. None of the ITS sequences present in these nine species matched those detected in any other species, which provides tentative evidence against recent introgression as an explanation. Rheum globulosum, previously indicated by cpDNA to represent an independent origin of decumbent habit, is indicated by ITS to be part of clade of decumbent species, which acquired cpDNA of another clade via hybridization. However decumbent and glasshouse morphology are confirmed to have arisen three and two times, respectively.
  
  
  CONCLUSIONS
  These findings suggested that hybridization among QTP species of Rheum has been extensive, and that a role of hybridization in diversification of Rheum requires investigation.
authors.affiliation: Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences , Lanzhou University, Lanzhou, Gansu, P. R. China.
authors.forename: Dongshi
authors.initials: D
authors.lastname: Wan
authors.affiliation: Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences , Lanzhou University, Lanzhou, Gansu, P. R. China ; College of Life Science, Sichuan University, Chengdu, Sichuan, P. R. China.
authors.forename: Yongshuai
authors.initials: Y
authors.lastname: Sun
authors.affiliation: Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences , Lanzhou University, Lanzhou, Gansu, P. R. China.
authors.forename: Xu
authors.initials: X
authors.lastname: Zhang
authors.affiliation: Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences , Lanzhou University, Lanzhou, Gansu, P. R. China.
authors.forename: Xiaotao
authors.initials: X
authors.lastname: Bai
authors.affiliation: Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences , Lanzhou University, Lanzhou, Gansu, P. R. China.
authors.forename: Jun
authors.initials: J
authors.lastname: Wang
authors.affiliation: Gansu Key Laboratory of Biomonitoring and Bioremediation for Environmental Pollution, School of Life Sciences , Lanzhou University, Lanzhou, Gansu, P. R. China ; School of Life and Sciences, Ludong University, Yantai, Shandong, P. R. China.
authors.forename: Ailan
authors.initials: A
authors.lastname: Wang
authors.affiliation: Institute of Molecular Plant Sciences, School of Biological Sciences, The University of Edinburgh, Edinburgh, United Kingdom.
authors.forename: Richard
authors.initials: R
authors.lastname: Milne
mesh_terms: D021901:DNA, Intergenic; D019143:Evolution, Molecular; D018628:Gene Dosage; D006824:Hybridization, Genetic; D008969:Molecular Sequence Data; D010802:Phylogeny; D011544:Pseudogenes; D011827:Radiation; D012250:Rheum / Q000145:classification / Q000235:genetics* / Q000528:radiation effects*; D017422:Sequence Analysis, DNA
chemical_list: D021901:DNA, Intergenic