Molecular Phylogeography Of Juniperus Przewalskii (Cupressaceae)

The Qinghai-Tibetan Plateau (QTP) is the most sensitive to the climatic changes in the world. The Quaternary climatic oscillation must have resulted in changes of the distributional ranges of the organisms occurring there. However, due to the arid environments and fewer accumulations of the related data, it remains unknown how these species survived in situ, retreated and recolonized as well as how the ecological systems changed correspondingly. The contrasting hypotheses had been proposed and no independent and solid evidence has been provided. In this study, based the DNA sequence variation at the population level, phylogeographic patterns were constructed for Juniperus przewalskii Kom., an endemic species to the QTP and a dominant species in the scattered forest communities.Two cpDNA fragments (trnT-trnF and trnS-trnG) were sequenced for 392 trees of 20 populations through the entire distribution range of the species. Six cpDNA haplotypes were identified (A, B, C, D, E and F). Significant population subdivision was detected (Gst = 0.772, Nst = 0.834), suggesting low levels of recurrent gene flow among populations and significant phylogeographic structure (Nst > Gst, P<0.05). Eight of the nine disjunct populations surveyed on the high-elevation northeast plateau were fixed for a single haplotype (A), while the remaining, more westerly population, contained the same haplotype at high frequency together with two low frequency haplotypes (C and F). In contrast, most populations that occurred at lower altitudes at the plateau edge were fixed or nearly fixed for one of two haplotypes, A or E. However, two plateau edge populations had haplotype compositions different from the rest. In one, four haplotypes (A, B, D and E) were present at approximately equivalent frequencies, which might reflect a larger refugium in the area of this population during the last glacial period. Phylogenetic analysis indicated that the most widely distributed haplotype A is not ancestral to other haplotypes. The edge regions remained as the refugia and these populations randomly fixed different haplotype due to bottleneck effects. Most platform populations probably derived commonly from the postglacial recolonization and their current disjunction occurred within Holocene because of the artificial or other factors. One unique haplotype of one population located in the central plateau suggested that this population survived the later glacial ages. These findings suggested that forests had appeared at a large scale in the northeastern plateau within the Holocene while the current alpine meadow or grasslands probably formed much later since then.In addition, based on the biotin capture method to enrich microsatellites of J. przewalskii, a total of 12 pairs of SSR primers with polymorphisms were developed.