Abstract
Reticulate evolution is considered to be among the main mechanisms of plant evolution, often leading to the establishment of new species. However, complex evolutionary scenarios result in a challenging definition of evolutionary and taxonomic units. In the present study, we aimed to examine the evolutionary origin and revise the species status of Campanula baumgartenii, a rare endemic species from the polyploid complex Campanula section Heterophylla. Morphometry, flow cytometric ploidy estimation, AFLPs, as well as chloroplast and nuclear DNA sequence markers were used to assess the morphological and genetic differentiation among C. baumgartenii, C. rotundifolia and other closely related taxa. Tetra- and hexaploid C. baumgartenii is morphologically and molecularly (AFLP) differentiated from sympatric C. rotundifolia. Contrasting signals from nuclear (ITS) and chloroplast (trnL-rpl32) markers suggest a hybrid origin of C. baumgartenii with C. rotundifolia and a taxon related to the alpine C. scheuchzeri as ancestors. Additionally, hexaploid C. baumgartenii currently hybridizes with co-occurring tetraploid C. rotundifolia resulting in pentaploid hybrids, for which C. baumgartenii serves as both seed and pollen donor. Based on the molecular and morphological differentiation, we propose to keep C. baumgartenii as a separate species. This study exemplifies that detailed population genetic studies can provide a solid basis for taxonomic delimitation within Campanula section Heterophylla as well as for sound identification of conservation targets.
Highlights
Interspecific hybridization is considered to be among the major forces of plant evolution (Arnold 1997)
Tetraploid C. baumgartenii was found in the Palatinate Forest only, while hexaploid individuals occurred in both distribution centres
Taxonomic status of C. baumgartenii Exploratory principal components analysis (PCA) based on morphometric data (Fig. 3) confirmed that morphological differences in Campanula sect
Summary
Interspecific hybridization is considered to be among the major forces of plant evolution (Arnold 1997). By introgression (backcrossing) of genes and genomes across species barriers, hybridization may lead to establishment of new species and eventually to the collapse of the parental taxa. It may affect local adaptation and selection processes (Mallet 2008). Intermediate characters are usually expected in hybrids, but hybrids often exhibit extreme phenotypes or novel characters, referred to as either ‘heterosis’ or ‘transgressive segregation’ (Rieseberg et al 1999)
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