A range-wide postglacial history of Swiss stone pine based on molecular markers and palaeoecological evidence

Aim: Knowing a species’ response to historical climate shifts
helps understanding its perspectives under global warming. We
infer the hitherto unresolved postglacial history of Pinus
cembra. Using independent evidence from genetic structure and
demographic inference of extant populations, and from palaeoecological
findings, we derive putative refugia and re-colonisation routes.
Location: European Alps and Carpathians. Taxa: Pinus
cembra. Methods: We genotyped nuclear and chloroplast
microsatellite markers in nearly 3,000 individuals from 147 locations
across the entire natural range of P. cembra. Spatial genetic
structure (Bayesian modelling) and demographic history (Approximate
Bayesian Computation) were combined with palaeobotanical records (pollen,
macrofossils) to infer putative refugial areas during the Last Glacial
Maximum (LGM) and re-colonisation of the current range.
Results: We found distinct spatial genetic structure, despite low
genetic differentiation even between the two disjunct mountain ranges.
Nuclear markers revealed five genetic clusters aligned East–West across
the range, while chloroplast haplotype distribution suggested nine
clusters. Spatially congruent separation at both marker types highlighted
two main genetic lineages in the East and West of the range. Demographic
inference supported early separation of these lineages dating back to a
previous interstadial or interglacial c. 210,000 years
ago. Differentiation into five biologically meaningful genetic clusters
likely established during post-glacial re-colonisation. Main
conclusions: Combining genetic and palaeoecological evidence
suggests that P. cembra primarily survived the LGM in
“cold period” refugia south of the Central European Alps and near the
Carpathians, from where it expanded during the Late Glacial into its
current Holocene “warm period” refugia. This colonisation history has led
to the distinct East–West structure of five genetic clusters. The two main
genetic lineages likely derived from ancient divergence during an
interglacial or interstadial. The respective contact zone (Brenner line)
matches a main biogeographic break in the European Alps also found in
herbaceous alpine plant species.