基于叶绿体DNA trnT-trnF序列研究祁连圆柏的谱系地理学

由于青藏高原的地貌效应,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。本文对这一地区特有分布物种祁连圆柏Juniperus przewalskii Kom.整个分布区内20居群392个个体的trnT-trnF序列变化进行了研究;共发现3种单倍型(haplotype),构成两种地理区域:高原台面上的居群主要固定Hap A,而Hap A、Hap B和Hap C在高原边缘居群均有分布。所有居群总的遗传多样性HT = 0.511,GST= 0.847。在低海拔的高原边缘,Hap A、Hap B和Hap C高频率固定在不同的居群中,表明可能存在多个不同的避难所,居群反复缩小和扩张的瓶颈效应造成了遗传多样性的丢失。而边缘的一个居群含有两种相似单倍型频率则可能是冰期后迁移融合而成或者该居群在冰期经受的瓶颈作用更弱。高原台面东部间断分布的居群只固定Hap A,表明它们可能经历了冰期后共同的回迁过程和由此产生的奠基者效应。我们的研究结果表明祁连圆柏在冰期可能存在多个避难所,瓶颈效应和奠基者效应造成了这些居群现在的遗传多样性分布式样。

Phylogeography of Juniperus przewalskii (Cupressaceae) inferred from the chloroplast DNA trnT-trnF sequence variation

The topological effect of the Qinghai-Tibet Plateau during the Quaternary climatic oscillation must have important effects on the patterns of spatial distribution and genetic structure of organisms distributed there. To obtain a better understanding of the historical dynamics of present-day species in this region, we examined the population structure of chloroplast trnT-trnF sequence variation in Juniperus przewalskii, an endemic tree species mainly distributed in the northeast plateau. Data were obtained for 392 trees from 20 populations covering the total distributional range of the species. Three cpDNA haplotypes were recorded and were structured into two geographical areas: haplotype A was present on the plateau platform, while all three haplotypes occurred along the plateau edge. Total genetic diversity, HT, was 0.511, with most variation distributed among rather than within populations (GST=0.847). Along the low altitudinal plateau edge, haplotypes A, B and C tended to be fixed or nearly fixed in different populations, indicating that the species may have survived the last glacial period in different refugia within this area, and the bottlenecks due to the repeated reduction and expansion of the population size resulted in the reduction of biodiversity. However, in one population both haplotypes occurred at intermediate frequencies, indicating the possibility of a contact zone or less strong bottleneck effect. On the eastern plateau platform, haplotype A was commonly fixed in the current disjunct populations, suggesting a common postglacial recolonization and a following founder effect. Our results indicate that there might exist in multi-glacial refugia in the plateau edge and both bottleneck and founder effects resulting from the repeated climatic oscillation combined had played important roles in shaping the current haplotype distribution pattern of this tree species.