Multiple ITS Copies Reveal Extensive Hybridization within Rheum (Polygonaceae), a Genus That Has Undergone Rapid Radiation

Dongshi Wan, Yongshuai Sun, Xu Zhang, Xiaotao Bai, Jun Wang, Ailan Wang*, Richard Milne

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

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.

Methodology/Principal Findings: 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.

Original languageEnglish
Article number89769
Number of pages10
JournalPLoS ONE
Volume9
Issue number2
DOIs
Publication statusPublished - 27 Feb 2014

Keywords

  • INTERNAL TRANSCRIBED SPACER
  • NUCLEAR RIBOSOMAL DNA
  • QINGHAI-TIBETAN PLATEAU
  • SPECIES-RICH GENUS
  • CONCERTED EVOLUTION
  • ADAPTIVE RADIATION
  • TRANSGRESSIVE SEGREGATION
  • PHYLOGENETIC INFERENCE
  • MAMMILLARIA CACTACEAE
  • MOLECULAR PHYLOGENY

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