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Background: Hybridisation is presumed to be an important mechanism in plant speciation and a creative evolutionary force often accompanied by polyploidisation and in some cases by apomixis. The Potentilla collina group constitutes a particularly suitable model system to study these phenomena as it is morphologically extensively variable, exclusively polyploid and expresses apomixis. In the present study, the alpine taxon Potentilla alpicola has been chosen in order to study its presumed hybrid origin, identify underlying evolutionary processes and infer the discreteness or taxonomic value of hybrid forms.
Results: Combined analysis of AFLP, cpDNA sequences and ploidy level variation revealed a hybrid origin of the P. alpicola populations from South Tyrol (Italy) resulting from crosses between P. pusilla and two cytotypes of P. argentea. Hybrids were locally sympatric with at least one of the parental forms. Three lineages of different evolutionary origin comprising two ploidy levels were identified within P. alpicola. The lineages differed in parentage and the complexity of the evolutionary process. A geographically wide-spread lineage thus contrasted with locally distributed lineages of different origins. Populations of P. collina studied in addition, have been regarded rather as recent derivatives of the hexaploid P. argentea. The observation of clones within both P. alpicola and P. collina suggested a possible apomictic mode of reproduction.
Conclusions: Different hybridisation scenarios taking place on geographically small scales resulted in viable progeny presumably stabilised by apomixis. The case study of P. alpicola supports that these processes played a significant role in the creation of polymorphism in the genus Potentilla. However, multiple origin of hybrids and backcrossing are considered to produce a variety of evolutionary spontaneous forms existing aside of reproductively stabilised, established lineages.
Chloroplasts are difficult to assemble because of the presence of large inverted repeats. At the same time, correct assemblies are important, as chloroplast loci are frequently used for biogeography and population genetics studies. In an attempt to elucidate the orientation of the single-copy regions and to find suitable loci for chloroplast single nucleotide polymorphism (SNP)-based studies, circular chloroplast sequences for the ultra-centenary reference individual of European Beech (Fagus sylvatica), Bhaga, and an additional Polish individual (named Jamy) was obtained based on hybrid assemblies. The chloroplast genome of Bhaga was 158,458 bp, and that of Jamy was 158,462 bp long. Using long-read mapping on the configuration inferred in this study and the one suggested in a previous study, we found an inverted orientation of the small single-copy region. The chloroplast genome of Bhaga and of the individual from Poland both have only two mismatches as well as three and two indels as compared to the previously published genome, respectively. The low divergence suggests low seed dispersal but high pollen dispersal. However, once chloroplast genomes become available from Pleistocene refugia, where a high degree of variation has been reported, they might prove useful for tracing the migration history of Fagus sylvatica in the Holocene.