Biogeography of Larches in North-East Siberia - using Single Nucleotide Polymorphisms derived by Genotyping by Sequencing

The present distribution pattern of Siberian boreal forests that are dominated by larches is to an unknown extent influenced by the glacial history. Here, we investigated whether we can observe patterns in the genetic variability of Siberian larches (Larix spp.) that can help us to unravel biogeographic migration routes since the Last Glacial Maximum (LGM). We revealed the spatial distribution of 14,003 Single Nucleotide Polymorphisms (SNPs) derived by Genotyping by Sequencing (GBS) in a subset of 148 larch individuals with a cluster analysis. To shed light on Larix’ postglacial migration routes, we applied an Approximate Bayesian Computation (using the software DIYABC). The results of the cluster analysis revealed the presence of three to four statistically verified clusters from Western to Eastern Eurasia that match well to the already expected distinction into the main larch species Larix sibirica, L. gmelinii and L. cajanderi. It can be discussed that under the light of ecological aspects and the spatial assignment to geographic regions, six clusters are plausible instead of the statistically derived most probable optimum of three to four main clusters. The tested hypotheses in DIYABC show that all present existing populations seem to be initiated far before the LGM. We presume that the different populations originate from larch populations that survived the glacial periods. Having the complex terrain in mind, we deduce that those individuals rather survived in refugia in the North, than migrated through complete recolonization from the South. The northernmost expansion during the Holocene seems to have benefitted from refugial populations ahead of the treeline, which explains the existence of Larix in the Far North although the treeline migration rates were slow. From our results, we expect that the present migration is probably slow at first, as there are currently no refugial populations far north, as there were probably in Holocene. But in the future, isolated trees in the tundra could become a starting point for rapid dispersal of boreal forests in the course of current climate warming.