A new Eurasian phylogeographical paradigm? Limited contribution of southern populations to the recolonization of high latitude populations in Juniperus communis L. (Cupressaceae).

Aim The aims of this population genetics study of the common juniper across Eurasia were to (1) assess the contribution of southern mountain ranges to the post-glacial recolonization of high latitudes and (2) test whether recent expansion or high gene flow could explain the low genetic differentiation in Northern Eurasia. Location Northern Eurasia and mountain regions of Central Europe and Asia. Methods Six hundred and twenty-two individuals were sampled in 42 populations. Two chloroplast DNA (cp DNA) fragments were investigated ( trnT- trnL and 16S- trnA). Analyses of the distribution of haplotypes across the continent included a suite of phylogeographical and phylogenetic tests. Putative geographical distribution in the past was reconstructed using environmental niche modelling. Results Eighty-four haplotypes clustered into four main clades ( GL1- GL4). The largest clade, GL3, corresponds to populations from the Alps, northern Europe, Western Caucasus and Siberia. These populations were moderately differentiated (28%) compared to the total range (76%) and Fu's F_s statistic was negative, indicating a population expansion. Some haplotypes within GL3 form subclades with a restricted geographical distribution, suggesting a local origin of the mutation and limited dispersal. In line with these findings, modelling of ecological niches found no significant reduction in the expected range during the LGM. Remarkably, populations from the eastern part of North Caucasus, the Himalayas, Tien Shan and south Siberia were distinctly different from populations in the rest of the range. Main conclusions As in Siberian larch species, the pattern of genetic diversity at cp DNA across the natural range of J. communis suggests that colonization of northern Europe and Siberia started from a limited area and predated the last glaciation. It is likely that juniper survived the subsequent glacial epoch at high latitudes in cryptic refugia serving as secondary centres of recolonization. Southern mountain refugia contribution to the recolonization of high latitudes was, at best, limited. [ABSTRACT FROM AUTHOR]