Influence of the Quaternary Glacial Cycles and the Mountains on the Reticulations in the Group Willkommia of the Genus Centaurea. trnT-trnL Centaurea

Group Willkommia of the genus Centaurea has been proposed to follow a model of reticulate evolution with recurrent hybridizations between divergent populations within the geographical range of a primary radiation, favored by the Pleistocene climatic oscillations and the rugged local topography. In this paper, we test the reticulation processes in Willkommia and the role of mountains in these processes by studying the genetic, demographic and geographic structure of populations of C. gadorensis, C. pulvinata, and C. sagredoi, three species of the group that due to their geographic distribution and previous molecular evidences represent a good system of study. Our results support that the current genetic structure of the populations of the three species is the result of historical gene flow in sites of secondary contact between species, during the glacial periods, and population isolation after the retraction of populations to the middle-upper areas of the mountains during the interglacials. The extension and direction of the gene flow was determined to a large extent by the situation of the populations in slopes oriented towards the same valley or towards different valleys, suggesting the intermountain valleys as the areas where secondary contacts occurred; and probably also because of the phylogenetic proximity of the taxa involved.