Cytoplasmic DNA variation does not support a recent contribution of Pinus sylvestris L. from the Caucasus to the main range

The history of the interaction between the boreal floras of northern Eurasia and those from the mountain areas located at intermediate latitudes remains insufficiently studied. Twenty-four population samples of 4 to 34 trees were analyzed with eight mitochondrial DNA (mtDNA) markers and four chloroplast DNA (cpDNA) microsatellite loci to study the history of Scots pine in the Black Sea region, and infer migration routes and genetic relationships with populations of the northern part of the range. These new data were combined with data previously obtained from Eastern Europe and North Asia. Scots pine past geographic range was also reconstructed using environmental niche modeling. Both mtDNA and cpDNA revealed a common origin of populations in the eastern Black Sea region (EBS), i.e., Crimea, Caucasus, and Asia Minor, and deep divergence from the main range of Scots pine, reminiscent of the isolation of enclaves in Iberian and Apennine Peninsulas. Mitochondrial DNA haplotypes (mitotypes) endemic to Western Caucasus are genetically intermediate between mitotypes from Eastern Europe and other mitotypes from the EBS region, indicating a recombinant origin likely due to migration to the Caucasus from the north and hybridization with local trees. Environmental niche modeling shows the possibility of such migration events during the last glacial maximum.