Welcome to migrants in a borderless Europe: bryophytes show the way to go

Abstract

Reconstructing the Quaternary history of European bryophytes has long been challenging because, except for macro-remains preserved in peat, the fossil record is extremely poor as compared to vascular plants. Coalescent simulations revealed that the postglacial assembly of European bryophytes involves a complex history from multiple sources, contrasting with the prevailing model of northwards species migration from Mediterranean refugia. A scenario of extra-European postglacial recolonization clearly emerged as dominant. A bulk of the bryoflora that pre-existed in Europe before the Ice Age was reinforced by allochthonous migrants. The Atlantic European fringe was, in contrast, de novo colonized by species primarily distributed across tropical areas. 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 temperate regions.