Biogeography of larches in eastern Siberia – using single nucleotide polymorphisms derived by genotyping by sequencing

The present distribution of Siberian boreal forests that are dominated by larches (Larixspp.) is influenced, to an unknown extent, by glacial history. Knowing the past treelinedynamics can improve our understanding of future treeline shifts under changingclimate. Here, we study patterns in the genetic variability of Siberian Larix to helpunravel biogeographic migration routes since the Last Glacial Maximum (LGM).We infer the spatial distribution and the postglacial demographic history of Larixusing genome-wide single nucleotide polymorphisms (SNPs) derived through geno-typing by sequencing (GBS) from 130 individuals sampled across eastern Siberia.Our analysis gives statistical support for two or three clusters, spanning from western toeastern Siberia. These clusters reveal a genetic structure influenced by isolation result-ing from geographical distance, barriers imposed by geographic features, and distinctglacial histories. Assuming three clusters, our demographic inference indicates that thecommon ancestor of the current Larix populations existed in northeast Siberia wellbefore the LGM. This suggests that Larix persisted in the northern region throughoutprevious glacials.Our genetic studies suggest that Larix likely survived the cold LGM in northern refu-gia, enabling a fast colonization of Siberia. Instead of complete repopulation fromsouthern areas postglacially, the northernmost Larix expansion during the Holoceneseems to have benefitted from refugial populations ahead of the treeline. Present-daymigration is expected to be slow initially, due to the absence of current refugial popula-tions in the far north, in contrast to the early-Holocene situation.