Abstract:

The uplift of the Qinghai-Tibetan Plateau and the cyclic fluctuation of the climate during the Quaternary Ice Age have greatly affected the distribution and genetic structure of plants and animals in this area and neighboring areas. Juema is an endemic plant of the Tibetan Plateau with high nutritional， medicinal， and ecological values. The taxonomic relationship and distribution of juema and Potentilla anserina are controversial in academia. Therefore， we conducted molecular genealogical and geographical analyses to explore the formation of genetic diversity in juema and to infer its migratory evolutionary history. We collected 810 individual plants from 30 populations and determined the sequences of their chloroplast trnL-trnF and nuclear internal transcribed spacer （ITS） regions. The data were analyzed to reveal the distribution of genetic variation within and among populations， and combined population genetics and phylogenetic analyses were conducted to determine the correlation between the genetic structure of the species and historical events. The aim of these analyses was to determine the evolutionary history of the species and the reasons for the current distribution pattern of different populations within the species. The main results were as follows： 1） Juema shows a high level of genetic diversity. Forty haplotypes^{of the cpDNA trnL-trnF fragment were detected， including 16 shared haplotypes， accounting for 40% of the total， and 24 population-specific haplotypes， accounting for 60% of the total （genetic diversity h=0.7078， haplotype diversity H_d=0.8217， nucleotide diversity π=0.010641， total genetic diversity H_T=0.849）. For the ITS region， 128 haplotypes were detected， including 42 shared haplotypes， accounting for 32.8% of the total， and 86 population-specific haplotypes， accounting for 67.2% of the total （h=0.7633， H_d=0.8168， π=0.003584， and H_T=0.844）. 2） Genetic diversity is greater within than among populations. Sequence analyses revealed high genetic diversity both within and among populations （cpDNA trnL-trnF： H_T=0.849， gene diversity within populations H_S=0.640； nrDNA ITS： H_T=0.844， H_S=0.763； H_T>H_S for both sequences）. The juema populations were divided into three groups： The Qinghai Plateau group， the Hengduan Mountains group， and the South Tibetan Valley group. The genetic variation of juema has mainly originated from within populations. 3） Juema populations show a distinct genealogical geographic structure. We conducted genetic polymorphism and geographic distribution pattern analyses based on the cpDNA trnL-trnF and nrDNA ITS data. For cpDNA trnL-trnF，the genetic differentiation coefficients were G_ST=0.246 and N_ST=0.417； for nrDNA ITS， G_ST=0.096 and N_ST=0.522. For both sequences， N_ST was significantly larger than G_ST （P<0.001）. The results were highly consistent between the two methods， and indicated that a significant spectral geographic structure exists in all population haplotypes of juema. Analysis of molecular variance （AMOVA） showed that the majority of genetic variation （59.69%） is within populations， with a high level of differentiation among populations （F_ST=0.40313）. 4） Both shared and endemic haplotypes are derived from ancient haplotypes. Centrally linked reticulation maps based on cpDNA trnL-trnF and nrDNA sequences showed a stellate structure with the shared haplotypes M₄ and H₉ at the center， and the shared haplotypes M₁ and M₃， and H₂， H₁₀， H₁₁， and H₁₂ at the trunk positions. The remaining shared and unique haplotypes were derived from these ancient haplotypes， and the results were consistent. 5） There has been a major expansion in the size and range of the plant population. When cpDNA trnL-trnF and nrDNA sequences were subjected to a manifold analysis， the former showed a single-peak curve in the manifold distribution， indicating that a large-scale expansion of the size and range of the population has occurred recently； and the latter showed a double-peaked curve， reflecting a high degree of complexity in its genetic genealogy. The results of Tajima’s D， Fu and Li’s D， and Fu and Li’s F tests were all negative and significant， and the statistical tests of sum of squares deviations and Harpending’s raggedness parameters were not significant， suggesting the possibility of recent expansion of juema populations. 6） Juema exists in three Ice Age refuges， i.e.， the Eastern Himalaya region， the southeastern edge of the Tibetan Plateau， and the Hengduan Mountains region.}

Key words: Potentilla anserina, chloroplast trnL-trnF fragment, nuclear gene ITS, Qinghai-Tibet Plateau, phylogeography