Perhaps there were northern refugia in LGM? The phylogeographic structure of the thermophilic tree Carpinus betulus in the Carpathian region.

Carpinus betulus L., the hornbeam, is a component of lowland and highland forests in Europe. By examining the postglacial migratory history of thermophilic tree species, the study aimed to unravel their putative glacial microrefugia in the Carpathian region. The present study points to the two distinct genetic AFLP groups of C. betulus in the Carpathian region that represent different genetic lineages based on Bayesian analysis. They differed in Nei's gene diversity index h, and the analysis of molecular variance AMOVA showed a percentage variation of the populations between the groups of 13.74 %. Principal coordinate analysis (PCoA) of 368 AFLP tree samples confirmed the presence of two genetic groups. Ninety-five populations underwent principal component analysis (PCA) to show the main correlations between genetic diversity indices and bioclimatic/climate variables (WorldClim and Carpatclim). The generalized logistic model (GLM) showed the significance of Nei's genetic index h in delimiting genetic groups. The results of population-genetic and multivariate analyses determined that the two genetic groups nowadays are spatially diffused and do not show a clear geographic pattern, pointing to a genetic melting pot. We found ecological links between genetic diversity and bioclimatic characteristics, especially the precipitation in the coldest quarter - Bio19. The refugial Maxent model indicates a significant contribution of the Bio7 variable (both linked with a continental type of climate) to the occurrence of the species during the LGM in Europe. We suggest the relict character of hornbeam populations in a specific climatic-terrain niche in the northern part of the Carpathian Basin.