Different speciation types meet in a Mediterranean genus: The biogeographic history of Cymbalaria (Plantaginaceae)

Abstract

Cymbalaria comprises ten species and six subspecies growing in rocky habitats in the Mediterranean Basin. Several features, such as the genus' highly fragmented distribution as well as noticeable ecological differentiation between partially sympatric species and presence of ploidy barriers between species suggest the involvement of different speciation types in its evolution. The aims of this study were to test the monophyly of Cymbalaria and to reconstruct infrageneric phylogenetic relationships, to infer the genus' biogeographic history by estimating divergence times and ancestral distribution areas of lineages, and to disentangle the role of different speciation types. To address these issues, we constructed a phylogeny with a complete taxon sampling based on ITS, 3'ETS, ndhF and rpl32-trnL sequences. We used the nuclear ribosomal DNA data to produce a time-calibrated phylogeny, which served as basis for estimating ploidy level evolution and biogeographic history. Cymbalaria was resolved as monophyletic. The genus originated ca. 4 Ma and three lineages segregated rapidly, one comprising solely C. microcalyx subsp. microcalyx and the other two corresponding to western and central-eastern species, respectively. The main diversification events occurred after the onset of the Mediterranean climate and during Pleistocene climate oscillations. Both founder-event speciation linked to long-distance dispersal events and sympatric speciation were supported by the biogeographic analyses. In addition, at least two polyploid speciation events were inferred. Finally, conflicts between current taxonomy and the phylogeny at the species and subspecies level clearly show the need of more detailed integrative taxonomic studies.