Testing reticulation and adaptive convergence in the Grimmiaceae (Bryophyta)
Abstract:Phylogenetic relationships based on plastid DNA sequences have recently been explored for the genus Grimmia, revealing a complex evolutionary history and many incongruities with respect to traditional views. Based on empirical observations it was postulated that episodes of allopolyploidy and various hybridization events have triggered speciation in the genus Grimmia. Comparisons of genes from different genomes could therefore help to detect putative reticulations that cannot be detected using a single genome. For this purpose phylogenetic inferences, based on the complete ITS region of nuclear ribosomal DNA, were contrasted with plastid (trnS-trnF, trnK/matK) derived ones. The ITS region proved to be highly variable in Grimmia, with various lineage-specific indels interspersed among a considerable number of conserved regions that contained important phylogenetic information. The sectional placement of most species is congruent with previous results based on plastid DNA. However, some species seemingly combine nuclear sequences of one section with chloroplast sequences of another. The species of Grimmia subg. Grimmia, with the exception of G. pulvinata, are nested within Grimmia in plastid phylogenies, but are sister to the remaining Grimmia groups and closer to Dryptodon based on nuclear DNA sequences. According to the Shimodaira-Hasegawa (SH) test an alternative hypothesis in which Grimmia subg. Grimmia is nested within Grimmia could be rejected. Similarly, an alternative topology with G. tergestina close to G. laevigata as revealed by plastid data was clearly rejected by the SH test, supporting the observation that G. tergestina appears to have the nuclear sequence of section Orthogrimmia and the chloroplast sequence of section Guembelia. We hypothesize that both cases can be best explained by past reticulation events.
Document Type: Research Article
Publication date: May 1, 2008
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