Premise of the Study

The origin of allopolyploids is believed to shape their evolutionary potential, ecology and geographical ranges. Morphologically distinct apomictic types sharing the same parental species belong to the most challenging groups of polyploids. We evaluated the origins and variation of two triploid taxa (Hieracium pallidiflorum, H. picroides) presumably derived from the same diploid parental pair (H. intybaceum, H. prenanthoides).

Methods

We used a suite of approaches ranging from morphological, phylogenetic (three unlinked molecular markers) and cytogenetic analyses (in situ hybridization) to genome size screening and genome skimming.

Key Results

Genotyping proved the expected parentage of all analyzed accessions of H. pallidiflorum and H. picroides and revealed that nearly all of them originated independently. Genome sizes and genome dosage largely corresponded to morphology whereas the maternal origin of the allopolyploids had no discernable effect. Polyploid accessions of both parental species usually contained genetic material from other species. Given the phylogenetic distance of the parents, their chromosomes appeared only weakly differentiated in GISH as well as in overall comparisons of the repetitive fraction of their genomes. Furthermore, the repeatome of a phylogenetically more closely related species (H. umbellatum) differed significantly more.

Conclusions

We proved (i) multiple origins of hybridogeneous apomicts from the same diploid parental taxa, and (ii) allopolyploid origins of polyploid accessions of the parental species. We also showed that the evolutionary dynamics of very fast evolving markers such as satellite DNA or transposable elements does not necessarily follow patterns of speciation.

Alignments of trnT-trnL and gsh1 sequences (Sanger sequencing) in fasta format generated manually in BioEdit. Missing data: N, gaps: dash

Data subjected to Maximum likelihood, Bayesian and Maximum parsimony analyses. Results presented in Figs. 8, 9 and Appendix S6 of the article.