Contributions of multiple refugia during the last glacial period to current mainland populations of Korean pine (Pinus koraiensis)

The northern microrefugia that existed during the Last Glacial Maximum (LGM) are a key factor in the demographic history of species. Pinus koraiensis has a unique distribution in northeast Asia. The Changbai Mountains and the Korean peninsula (CM/KP) are usually considered to be the LGM refugia for P. koraiensis. However, the Xiaoxingan Range (XR), at the northern part of this species' distribution, is another possible refugium. We used chloroplast sequencing and ten nuclear single-copy gene loci to calculate the genetic diversity pattern of P. koraiensis. The probabilities of a single LGM refugium and of multiple LGM refugia were calculated based on approximate Bayesian computation. The effect of the latitudinal gradient on genetic diversity was not significant. However, unique alleles occurred at low frequencies in CM/KP and XR. A conservative estimate of the coalescence time between CM/KP and XR is 0.4 million years ago, a time prior to the LGM. Gene flow between CM/KP and XR was estimated to be more than one in per generation, an amount that may be sufficient to limit genetic divergence between the regions. Our study strongly supports the hypothesis that XR was another LGM refugium in addition to CM/KP.