Influence of the Quaternary Glacial Cycles and the Mountains on the Reticulations in the Subsection Willkommia of the Genus Centaurea

Late Neogene and Quaternary climatic oscillations have greatly shaped the genetic structure of the Mediterranean Basin flora, with mountain plant species tracking warm interglacials/cold glacials by means of altitudinal shifts instead of broad latitudinal ones. Such dynamics may have enhanced population divergence but also secondary contacts. In this paper, we use a case example of subsection Willkommia of Centaurea (comprising three narrowly distributed endemic species, Centaurea gadorensis, C. pulvinata, and C. sagredoi) to test for reticulate evolution and recurrent hybridizations between nearby populations. For this, we combine analyses of genetic diversity and structuring, gene flow and spatial correlation, and ecological niche modeling. Our results support the contention that the current genetic structure of the three species is the result of historical gene flow at sites of secondary contact during the glacial periods, followed by isolation after the retraction of populations to the middle-upper areas of the mountains during the interglacial periods. The extent and direction of the gene flow was determined largely by the location of the populations on mountainsides oriented toward the same valley or toward different valleys, suggesting the intermountain valleys as the areas where secondary contacts occurred.

This research was supported by a Technical Assistance agreement between E.G.M.A.S.A. (Empresa de Gestión Medioambiental S. A., Consejería de Medio Ambiente, Junta de Andalucía) and the University of Granada (ref. NET699759), by the Spanish Ministry of Science and Innovation (Project CGL2007- 60781/BOS), the Generalitat de Catalunya (“Ajuts a Grups de Recerca Consolidats” 2009/SGR/00439 and 2017-SGR1116), and the CSIC (“Proyecto Intramural Especial” grant no. 200730i035 awarded to RV and JAE-Doc contract to JL-P). SB-MS received a Beca-Colaboración grant from the Spanish Ministry of Education and a Beca-Iniciación a la Investigación grant from the University of Granada.