Survival in nunatak and peripheral glacial refugia of three alpine plant
species is partly predicted by altitudinal segregation
Abstract
Mountain biota survived the Quaternary cold stages in peripheral refugia
and/or ice-free peaks within ice-sheets (nunataks). While survival in
peripheral refugia has been broadly demonstrated, evidence for nunatak
refugia is still scarce. We generated RADseq data from three mountain
plant species occurring at different elevations in the southeastern
European Alps to investigate the role of different glacial refugia
during the Last Glacial Maximum (LGM). We tested the following
hypotheses. (i) The deep Piave Valley forms the deepest genetic split in
the species distributed across it, delimiting two peripheral refugia.
(ii) The montane to alpine species Campanula morettiana and Primula
tyrolensis survived the LGM in peripheral refugia, while high-alpine to
subnival Saxifraga facchinii likely survived in several nunatak refugia.
(iii) The lower-elevation species suffered a strong population decline
during the LGM. By contrast, the higher-elevation species shows
long-term stability of population sizes due to survival on permanently
ice-free peaks and small population sizes at present. We found
peripheral refugia on both sides of the Piave Valley, which acted as a
major genetic barrier. Demographic modeling confirmed nunatak survival
not only for S. facchinii, but also for montane to alpine C. morettiana.
Altitudinal segregation influenced the species’ demographic
fluctuations, with the lower-elevation species showing a significant
population increase at the end of the LGM, and the higher-elevation
species either showing decrease towards the present or stable population
sizes with a short bottleneck. Our results highlight the role of nunatak
survival and species ecology in the demographic history of mountain
species.