Patterns of reticulate evolution in the Dactylorhiza (Orchidaceae) polyploid complex in Western Europe
(2004)
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- Hybridization and polyploidization have received great attention from scientists and are known to act as a creative force in plant evolution. Molecular phylogenetic reconstruction has been and will continue to be a powerful tool for inferring natural hybridization, introgression and polyploid speciation among plants. Combined evidence from differently inherited markers such as chloroplast DNA (cpDNA), nuclear ribosomal DNA (nrDNA) and low or single copy nuclear genes are usually used to determine the parental origins and reconstruct evolutionary histories of polyploids. In Europe, the genus Dactylorhiza comprises a bewildering variety of forms that are difficult to sort into discrete taxa. Most Dactylorhiza species are diploid or tetraploid and combined evidence from cytological, morphological and allozyme data suggest that the evolution of this genus is highly reticulated. The principal objective of this thesis is to unravel polyploid evolution in the genus Dactylorhiza in Western Europe using a phylogenetic approach based on chloroplatic and nuclear ribosomal DNA markers. Eight tetraploid species (i.e. Dactylorhiza majalis, D. praetermissa, D. elata, D. angustata, D. brennensis, D. sphagnicola, D. traunsteineri and D. maculata) and their putative diploid progenitors were sampled in multiple populations in Western Europe, sequenced for the nuclear ribosomal DNA, and analysed by PCR-RFLP for the chloroplast DNA. Using PCR-RFLP analysis, four highly differentiated chloroplast DNA lineages were identified. Eighty percent of the chloroplast variation were consistent with currently accepted species boundaries. Our results provide strong evidence that the allotetrapolyploid species sampled have been formed through asymmetric hybridization with a member of the D. fuchsii/maculata group as the maternal parent. The phylogenetic tree based on sequences of both Internal and External transcribed spacer of the 18S - 26S nuclear ribosomal DNA (ITS and ETS, respectively) suggests that three diploid lineages and one autotetraploid lineage have been involved in the formation of the allotetrapolyploid taxa investigated. Cloned sequences and the topology of the ITS plus ETS tree indicate that the allotetraploid species D. elata, D. brennensis, and D. sphagnicola have originated from the autotetraploid lineage formed by D. maculata together with the D. incarnata lineage. On the other hand, D. majalis and D. angustata seem to have been formed, together with D. incarnata, by the the diploid lineage represented by D. fuchsii. Finally, the D. saccifera lineage seems to have been involved together with the D. incarnata lineage in the formation of D. preatermissa.
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Devos, N. (2004). Patterns of reticulate evolution in the Dactylorhiza (Orchidaceae) polyploid complex in Western Europe. https://hdl.handle.net/2078.5/98448