Bienvenida a los migrantes a una Europa sin fronteras: los briófitos muestran el camino a seguir

Abstract

Reconstructing the Quaternary history of European bryophytes has long been challenging issue because, except for macro-remains preserved in peat, the fossil record is extremely poor as compared to vascular plants. Coalescent simulations, for which an introductory overview is presented, revealed that the postglacial assembly of European bryophytes involves a complex history from multiple sources, contrasting with the prevailing model in which species migrated northwards from southern refugia. A scenario of extra-European postglacial recolonization clearly emerged as dominant. Such a substantial contribution of allochthonous migrants in the postglacial assembly of European bryophyte floras is unparalleled in other plants and animals. For the bulk of the flora, allochtonous migrants reinforced small populations of species that pre-existed in Europe before the Ice Age. The Atlantic fringe of the European continent was, in contrast, de novocolonized by species primarily distributed across tropical areas, which migrated towards the Macaronesian islands where they often speciated, before ending their colonization pathway in western Europe. We hypothesize that, for the particular case of the oceanic bryophyte floristic element, the Macaronesian islands represented a mandatory stepping-stone situated midway between the tropics and Europe due to the necessity for tropical species to pre-adapt under insular warm-temperate conditions before they successfully establish in colder temperate continental regions.