基于叶绿体DNA trnL-F序列研究肋果沙棘的谱系地理学

由于青藏高原的地理效应,第四纪冰期气候的反复变化应对现今该地区生物的地理分布及其居群遗传结构产生重大影响。肋果沙棘Hippophae neurocarpa是青藏高原地区的一个特有种,根据叶上的附属物（星状鳞毛或者鳞片状鳞毛）分为两个亚种：肋果沙棘亚种subsp.neurocarpa和密毛肋果沙棘亚种subsp.stellatopilosa。依据母系遗传的叶绿体DNA片段对该物种谱系地理学进行研究不仅能阐明该物种冰期避难所,而且对于理解两个亚种的母系分化也具有重要意义。共对两个亚种14居群的70个个体的trnL-F序列进行了测序,共发现8种单倍型,其中5种单倍型出现在肋果沙棘亚种中,4种出现在密毛肋果沙棘亚种中,两个亚种共享一种单倍型。种内谱系分化与两个亚种形态上的分化不一致。嵌套进化分支把8种单倍型分为三支：一支为肋果沙棘亚种,其他两支中两个亚种单倍型嵌套组成,且肋果沙棘亚种处于进化末端。我们的研究结果还表明肋果沙棘在冰期可能在高海拔地区存在多个避难所,并且存在来自避难所的邻域扩张。

Phylogeography of Hippophae neurocarpa (Elaeagnaceae) inferred from the chloroplast DNA trnL-F sequence variation

The topological effect of the Qinghai-Tibetan Plateau during the Quaternary climatic oscillation must have important effects on spatial distribution and genetic structure of organisms distributed there. At the same time, the ecological niches provided by the uplifts of the plateau and the following Quaternary climatic changes may have promoted morphological differentiation and speciation of plants occurring there. The plateau endemic Hippophae neurocarpa (Elaeagnaceae) is a dominant shrub species along the streams or rivers and it also occurs in the semiarid ecosystem. This species is recognized as two separate subspecies, i.e. ssp. neurocarpa and ssp. stellatopilosa, mainly according to the appendages on leaves and different habitat preferences. The former is characteristic of scale-like appendages on the leaves and distributed in the drier and colder habitats while the latter has stellate hairs with a preference of occurring in the wetter and warmer habitats. It is interesting to know whether the morphological sub-speciation of H. neurocarpa is correlated with the intra-specific chloroplast phylogeny. In addition, this species also provide a good proxy to test the hypothesis that a few cold- or dry-tolerating species survive in the high altitude region of the plateau during the Quaternary glacial stages. In this study, we examined chloroplast trnL-F sequence variation from both subspecies of H. neurocarpa. The chloroplast genome was found to be maternally inherited in Hippophae and the intraspecific genealogy may reflect the maternal lineage sorting between both subspecies. A total of eight haplotypes were recovered through sequencing 70 individuals from 14 populations. One was shared by both subspecies, and four and three were only found in ssp. neurocarpa and ssp. stellatopilosa respectively. These findings suggested that two subspecies did not show genealogical concordance with morphological differentiation in this fragment. The constructed nested cladogram classified eight haplotypes into three lineages: one consisted of endemic haplotypes of ssp. neurocarpa and the other two included haplotypes from both subspecies with those of ssp. neurocarpa at the tip positions. In addition, the unique haplotypes recovered in the high altitude suggested that this species might have survived in these arid habitats. The contiguous range expansion was detected from these different refugia.