[en] Current biodiversity patterns in the northern hemisphere have primarily been shaped by
climatic fluctuations that took place during the Pleistocene. While the identification of
glacial refugia and post-glacial migration routes has long been a major focus in historical
biogeography, the question of where species currently restricted to Alpine areas persisted
during glaciations has long appeared as a striking puzzle. This question is particularly
timely as it impacts our understanding of the speed at which organisms migrated to track
areas of suitable climate, with substantial implications regarding their ability to face the
current velocity of climate change. Using RAD sequencing data for selected land plant
species (bryophytes, pteridophytes, spermatophytes), we determine whether current
distribution patterns result from the in-situ persistence of populations under the ice or
migrations from ice-free refugia. We further assess the rate at which migrations effectively
occurred, and how these rates differ within and among biota characterized by contrasting
dispersal syndromes using coalescence simulations. Bryophytes and spermatophytes
exhibited contrasted patterns of genetic structure, consistent with their dispersal
capacities. Although the analyses revealed different biogeographic origins for species
currently distributed across the Alps, observed genetic structure and diversity were
globally largely consistent across taxa with simulations under a scenario of persistence
within the Alps. Spatially explicit models of coalescence were finally implemented,
considering movements of individuals and genes while attempting to connect current
patterns of genetic variation with the evolution of the species range over time. We aim to
determine whether back-colonisation took place from ice-free refugia at the southern
limit of the mountain range or from ice-covered areas within the core of it, and at which
rate. This spatially explicit framework points to different recolonization scenario accross
species, evidencing that some species could have survived under the ice sheet and back
colonized the Alps lower than thought.
