Evolutionary history and genetic diversity of apomictic allopolyploids in Hieracium s.str. (Asteraceae): morphological versus genomic features

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.