Phylogeography Of Juniperus Sabina L. (Cupressaceae)

The climatic oscillations during the Quaternary have seriously affected the range distribution and current diversity of all plants occurring over the world especially those in the temperate regions.Phylogeography was developed to elucidate these patterns,processes and factors based on the molecular signals,for example,identifying the glacial refugia and tracing the postglacial recolonizations.Chloroplast(cp)DNA is inherited in a single parent and widely used to phylogeographical studies of plants due to its rare recombination.In this study, phylogeographical patterns of Juniperus sabina occurring in the north China and Xinjiang was analysed with aims to elucidate both the present-day geographical distribution of populations and the response to the Quaternary climatic oscillations of this species.Three cpDNA fragments,i.e.,trnL-trnF,trnS-trnG and trnD-trnT,were sequenced for 132 trees of 15 populations.Five cpDNA haplotypes were identified. Significant population subdivision was detected(G_ST= 0.926,N_ST= 0.980), suggesting low levels of recurrent gene flow among populations and significant phylogeographic structure(N_ST＞G_ST,P＜0.05).Five haplotypes showed no overlapping distribution.Eight of the nine populations surveyed in north China were fixed for a single haplotype A except for one in Mu Us Desert that contained another haplotype D with a low frequency.In contrast,five of six populations in Xinjiang were fixed for a single haplotype B while another population from Yili contained two other haplotypes C and E.Phylogenetic analyses of six haplotypes clustered into three clades which are consistent with their respective distributions in the three regions.These analyses suggest that a long period of allopatric fragmentation between populations of this species in three regions and the independent refugia had been maintained for each region during the Quaternary climatic oscillations and the current populations of each region experienced a common postglacial recolonization. This fast recolonization resulted in the fixture of relatively poor diversity due to the founder effects and possibly also because of the bottleneck effects during the repeated cycles of the climatic oscillations.Additionally,this study also suggests that both J.davurica and one population of J.chinensis(growing in the Qinghai Lake)are conspecific to J.sabina and supports the recent taxonomic revisions of these three taxa.