Genetic variation of Scots pine (Pinus sylvestris L.) in Eurasia: impact of postglacial recolonization and human-mediated gene transfer

Abstract Key message The range-wide level of genetic variation of Scots pine ( Pinus sylvestris L.) is geographically structured. High admixture and low genetic structure of populations in Central Europe and Fennoscandia suggest past recolonization from multiple sources and the influence of human-mediated gene transfer. Gene pools of marginal and isolated stands require active conservation. Some areas of Scots pine distribution need further genetic studies. Context Scots pine ( Pinus sylvestris L.) seems to be a species of low conservation priority because it has a very wide Eurasian distribution and plays a leading role in many forest tree breeding programs. Nevertheless, considering its economic value, long breeding history, range fragmentation, and increased mortality, which is also projected in the future, it requires a more detailed description of its genetic resources. Aims Our goal was to compare patterns of genetic variation found in biparentally inherited nuclear DNA with previous research carried out with mitochondrial and chloroplast DNA due to their different modes of transmission. Methods We analyzed the genetic variation and relationships of 60 populations across the distribution of Scots pine in Eurasia (1262 individuals) using a set of nuclear DNA markers. Results We confirmed the high genetic variation and low genetic differentiation of Scots pine spanning large geographical areas. Nevertheless, there was a clear division between European and Asian gene pools. The genetic variation of Asian populations was lower than in Europe. Spain, Turkey, and the Apennines constituted separate gene pools, the latter showing the lowest values of all genetic variation parameters. The analyses showed that most populations experienced genetic bottlenecks in the distant past. Ongoing admixture was found in Fennoscandia. Conclusions Our results suggest a much simpler recolonization history of the Asian than European part of the Scots pine distribution, with migration from limited sources and possible founder effects. Eastern European stands seem to have descended from the Urals refugium. It appears that Central Europe and Fennoscandia share at least one glacial refugium in the Balkans and migrants from higher latitudes, as well as from south-eastern regions. The low genetic structure between Central Europe and Fennoscandia, along with their high genetic admixture, may result at least partially from past human activities related to the transfer of germplasm in the nineteenth and early twentieth centuries. In light of ongoing climate changes and projected range shifts of Scots pine, conservation strategies are especially needed for marginal and isolated stands of this species. Genetic research should also be complemented in parts of the species distribution that have thus far been poorly studied.