title: The phylogeography of Eurasian Fraxinus species reveals ancient transcontinental reticulation.
abstract: To investigate the biogeographical history of ashes species of the Eurasian section Fraxinus and to test the hypothesis of ancient reticulations, we sequenced nuclear DNA (nETS and nITS, 1075 bp) for 533 samples and scored AFLP for 63 samples of Eurasian ashes within the section Fraxinus. The nITS phylogeny retrieved the classical view of the evolution of the section, whereas nETS phylogeny indicated an unexpected separation of F. angustifolia in two paraphyletic groups, respectively found in southeastern Europe and in the other parts of the Mediterranean basin. In the nETS phylogeny, the former group was closely related to F. excelsior, whereas the later was closely related to F. mandshurica, a species which is restricted nowadays to northeastern Asia. This topological incongruence between the two loci indicated the occurrence of an ancient reticulation between European and Asian ash species. Several other ancient reticulation events between the two European species and the other species of the section were supported by the posterior predictive checking method. Some of these reticulation events would have occurred during the Miocene, when climatic variations may have lead these species to expand their distribution range and come into contact. The recurrent reticulations observed among Eurasian ash species indicate that they should be considered as conspecific taxa, with subspecific status for some groups. Altogether, the results of the present study provide a rare documented evidence for the occurrence of multiple ancient reticulations within a group of temperate tree taxa with modern disjunct distributions in Eurasia. These ancient reticulation events indicate that the speciation process is slow in ashes, necessitating long periods of geographical isolation. The implications for speciation processes in temperate trees with similar life history and reproductive biology are discussed.
authors.affiliation: AgroParisTech, UMR 8079, 91405 Orsay, France; Centre national de la recherche scientifique, UMR 8079, 910405 Orsay, France; Université Paris-Sud, UMR 8079, F-91000 Orsay, France; Chaire de recherche du Canada en génomique forestière et environnementale, Centre d'étude de la forêt et Institut de biologie intégrative et des systèmes, Université Laval, Québec, Québec G1V 0A6, Canada. Electronic address: damien.hinsinger@u-psud.fr.
authors.forename: Damien D
authors.initials: DD
authors.lastname: Hinsinger
authors.affiliation: Muséum National d'Histoire Naturelle, UMR CNRS 7205 'Origine, Structure et Evolution de la Biodiversité', 16 rue Buffon, CP 39, F-75005 Paris, France. Electronic address: gaudeul@mnhn.fr.
authors.forename: Myriam
authors.initials: M
authors.lastname: Gaudeul
authors.affiliation: Genoscope, Centre National de Séquençage, 2 rue Gaston Crémieux, CP 5706, F-91057 Evry Cedex, France. Electronic address: acouloux@genoscope.cns.fr.
authors.forename: Arnaud
authors.initials: A
authors.lastname: Couloux
authors.affiliation: Chaire de recherche du Canada en génomique forestière et environnementale, Centre d'étude de la forêt et Institut de biologie intégrative et des systèmes, Université Laval, Québec, Québec G1V 0A6, Canada. Electronic address: jean.bousquet@sbf.ulaval.ca.
authors.forename: Jean
authors.initials: J
authors.lastname: Bousquet
authors.affiliation: AgroParisTech, UMR 8079, 91405 Orsay, France; Centre national de la recherche scientifique, UMR 8079, 910405 Orsay, France; Université Paris-Sud, UMR 8079, F-91000 Orsay, France. Electronic address: nathalie.frascaria@u-psud.fr.
authors.forename: Nathalie
authors.initials: N
authors.lastname: Frascaria-Lacoste
mesh_terms: D000352:Africa, Northern; D018744:DNA, Plant / Q000235:genetics; D005060:Europe; D031661:Fraxinus / Q000235:genetics*; D010802:Phylogeny; D058974:Phylogeography; D017422:Sequence Analysis, DNA
chemical_list: D018744:DNA, Plant
keywords: AFLP; Geographic disjunction; Reticulate evolution; Topological incongruence; nETS; nITS