喜马拉雅-横断山区优越虎耳草谱系地理学研究

利用叶绿体DNA非基因编码区rpl20-rps12和trnL-trnF作为分子标记，对喜马拉雅-横断山区优越虎耳草13个居群151个个体进行谱系地理学研究，旨在揭示优越虎耳草现有的遗传结构及其演化历程。共检测到19个单倍型，其中63%的单倍型为居群特有单倍型。研究还发现，优越虎耳草居群总的遗传多样性较高（H_t=0.868），居群内平均遗传多样性较低（H_s=0.466）。分子变异分析（AMOVA）表明，优越虎耳草居群57.37%的遗传变异来自居群内，居群间遗传变异为42.63%。居群遗传分化系数N_st大于G_st（N_st=0.463，G_st=0.438，P>0.05），但不显著，表明优越虎耳草在其整个分布范围内没有明显的谱系地理结构。中性检验结果表明，Tajima's D为负值（-1.348 32，P>0.05）而Fu's F_s*为正值（18.915 72，P>0.05），但均不显著，结合歧点分布分析发现该物种在整个分布范围内未经历过居群扩张。此外，在本研究中优越虎耳草遗传多样性和核苷酸多样性较高的居群及大量特有单倍型在整个分布范围内随机分布，符合"微型避难所"假说。优越虎耳草居群在冰期可能随气候波动而发生分布范围的不断变化，最终在相互隔离的"高山岛屿"中发生异域分化，导致大量特有单倍型产生。因此，推测优越虎耳草与其生境中的乔木和灌木可能具有相似的谱系地理历史，它们可为优越虎耳草提供微型避难所而使之在冰期时保留下来。

Phylogeography of Saxifraga egregia in Himalaya-Hengduan Mountains

The experiment was conducted to studygenetic structure and phylogeographic history of Saxifraga egregia, by using two chloroplast DNA sequences, rpl20-rps12 and trnL-trnF, and a sampling strategy of 151 individuals from 13 populations in the Himalaya-Hengduan Mountains. Nineteen haplotypes(H1-H19) were detected based on the concatenated sequences of rpl20-rps12 and trnL-trnF. Haplotype H2 was wide-spread across the distribution range of S.egregia, while 63% were private haplotypes. Genetic structure analysis detected a high level of total gene diversity(H_t=0.868), however, average within-population diversity was relatively low(H_s=0.466).By analysis of molecular variance, 57.37% of the total variation was described as within-population variation, while among-population variation was represented as 42.63%. An estimation of non-significantly larger N_st(0.463) than G_st(0.438,P>0.05) value suggested an absence of phylogeographic structure across the whole distribution range of S.egregia. Recent range expansion or demographic expansion at the level of total gene pool of S.egregia were rejected according to neutrality tests and mismatch distribution analysis. Genetic signal of a stochastic distribution of private haplotypes, as well as populations with high gene diversity and nucleotide diversity, suggesting the existence of multi-microrefugia of S.egregia during Quaternary glaciations. Repeated expansion and contraction of distribution range of S.egregia during Quaternary glaciations could have finally fragmented its distribution range into isolated "alpine islands", and have facilitated allopatric divergence, resulting in the formation of high proportion of private haplotypes across the distribution range of S.egregia. It has been reported that some trees and shrubs inhabited by S.egregia showed multi microrefugiain the Qinghai-Tibetan Plateau during Quaternary glaciations, which may have provided suitable micro-environment for the in situ survival of S.egregia during glacials.