Hybridization and introgression are prevalent in Southern European Erysimum (Brassicaceae) species

This research is supported by grants from FEDER/Junta de Andalucia-Consejeria de Economia y Conocimiento A-RNM505-UGR18 and P18-FR-3641. This research was also funded by the Spanish Ministry of Science and Innovation (CGL201679950-R and CGL2017-86626-C2-2-P), including EU FEDER funds. C.O.M. was supported by the Ministry of Economy and Competitiveness (BES-2014-069022).Background and Aims: Hybridization is a common and important force in plant evolution. One of its outcomes is introgression - the transfer of small genomic regions from one taxon to another by hybridization and repeated backcrossing. This process is believed to be common in glacial refugia, where range expansions and contractions can lead to cycles of sympatry and isolation, creating conditions for extensive hybridization and introgression. Polyploidization is another genome-wide process with a major influence on plant evolution. Both hybridization and polyploidization can have complex effects on plant evolution. However, these effects are often difficult to understand in recently evolved species complexes. Methods: We combined flow cytometry, transcriptomic and genomic analyses, and pollen-tube growth assays to investigate the consequences of polyploidization, hybridization, and introgression on the recent evolution of several Erysimum (Brassicaceae) species from the South of the Iberian Peninsula, a well-known glacial refugium. This species complex differentiated in the last 2Myr, and its evolution has been hypothesized to be determined mainly by polyploidization, interspecific hybridization, and introgression. Key Results: Our results support a scenario of widespread hybridization involving both extant and “ghost” taxa. Several taxa studied here, most notably those with purple corollas, are polyploids, likely of allopolyploid origin. Moreover, hybridization in this group might be an ongoing phenomenon, as prezygotic barriers appeared weak in many cases. Conclusions: The evolution of Erysimum spp. has been determined by hybridization to a large extent. The adaptive value of such genomic exchanges remains unclear, but our results indicate the importance of hybridization for plant diversification across evolutionary scales.FEDER/Junta de Andalucia-Consejeria de Economia y Conocimiento A-RNM505-UGR18 P18-FR-3641Spanish Government CGL201679950-R CGL2017-86626-C2-2-PEuropean CommissionMinistry of Economy and Competitiveness BES-2014-06902