Resolving the taxonomy and evolution of the Erysimum odoratum (Brassicaceae) species complex in the Carpathians and adjacent regions

Richard Bačák ¹, Marek Šlenker ¹

Plant Science and Biodiversity Center, Slovak Academy of Science, Bratislava ¹

Erysimum is an evolutionarily difficult genus with a high species diversity, several basic chromosome numbers, frequent occurrence of polyploidy and hybridization. In our study, we focus on the taxonomy and evolution of the Erysimum odoratum species group, which consists of up to nine biennial species distributed in the Carpathians and the western Balkan Peninsula. Our aim is to investigate their karyological variation, phylogenetic relationships and morphological differentiation. Using genome-wide RADseq data, we found that this species complex is polyphyletic, as it is divided into one predominantly Carpathian and three Balkan clades. Here, we focus on the Carpathian clade, where we observed significant variation in genome size, indicating the presence of different cytotypes and ploidy levels beyond previously known chromosome number reports. In the most widespread species E. odoratum s.str., we confirmed the tetraploid cytotype with 2n=32, but also discovered a cytotype with 2n=22 occurring disjunctively in the Papuk Mts. (northeastern Croatia) and in Porțile de Fier (southwestern Romania). Preliminary cytogenomic analyses suggest its tetraploid level despite the reduced chromosome number, which is probably due to the post-polyploid descending dysploidy. Additionally, populations in the Fruška Gora Mts. (Serbia) exhibited high DNA content, suggesting a hexaploid cytotype. In contrast, we did not confirm the presence of diploid cytotype for E. odoratum s.str. Instead, both phylogenomic and morphological evidence suggest that the diploids assigned to this species from the Western Carpathians actually belong to E. witmannii s.l., which comprises up to three species (E. witmannii s.str., E. pallidiflorum and E. transsilvanicum) reported as endemic to the Carpathians Mts. In E. witmannii s.l. we confirmed the common cytotype with 2n=14, but also discovered two other, previously unknown cytotypes in the Southern Carpathians: one with 2n=16 in the Piatra Craiului and Bucegi mountains and another (with a different genome size, but as yet undetermined chromosome number) in the Retezat Mts. To assess morphological variation, we measured a total of 32 morphological characters in 74 sampled populations and nearly 300 cultivated individuals. Morphological differentiation between the Carpathian populations of E. witmannii s.l. (considering traditionally recognized species, cytotypes, genetic and geographic groupings) was low, while the tetraploid E. odoratum s.str. was well distinguishable. RADseq analyses of E. witmannii s.l. show geographic rather than taxonomic structure, suggesting that isolation by distance contributes to differentiation within the complex and calls into question the recognition of three separate species. The observed patterns suggest that the evolution of the studied species complex is also shaped by large-scale chromosomal rearrangements and proliferation of repetitive DNA, which will be investigated in the future.

Main author career stage: PhD student

Contribution type: Talk

First choice session: 1. Systematics, phylogenetics, biogeography and evolution

Second choice session: 5. Genetics, genomics, and bioinformatics