Format: ORAL

Lara Wootton1 Florian Boucher1 Sbastien Lavergne1

1 Université Grenoble-Alpes

How past orogeny, landscape dynamics and climate change drove the emergence of species-rich mountain floras remains poorly understood. Here, we aim to uncover how the physical history of a range influences the assembly of its biodiversity in the context of the European Alpine sky island (ASI) flora. Using newly sequenced chloroplast genomes for 96% of the flora, we reconstruct a time-calibrated phylogenetic tree to infer temporal changes in assembly rates. We show that the majority of the flora assembled via colonisation rather than diversification, and experienced high rates of extinction over the course of its evolution. The accumulation of extant lineages was decoupled from major orogenic events, such as the initial uplift of the Alps and the later rise of the peripheral massifs. Most ASI lineages instead originated within the last 5 Myr. The Quaternary climate oscillations had the strongest impact on colonisation and diversification rates, which increased substantially during the Pleistocene glacial cycles. A search of existing biogeographic literature showed that many ASI lineages originated locally in Europe, rather than through long distance dispersal from temperate Asian ranges. We conclude that the ASI flora consists of a continuous subset of the European flora, potentially filtered by the ability to disperse into the sky islands after the disturbance of the Pleistocene glacial cycles. Our findings contradict established theories of Alpine plant biogeography, likely because by analysing the entire flora we include species-poor lineages that comprise an overlooked, but important, component of the flora.