Qiao Cai-Yuan, Ran Jin-Hua, Li Yan, Wang Xiao-Quan
State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, China.
Ann Bot. 2007 Sep;100(3):573-80. doi: 10.1093/aob/mcm134. Epub 2007 Jul 4.
Cedrus (true cedars) is a very important horticultural plant group. It has a disjunct distribution in the Mediterranean region and western Himalaya. Its evolution and biogeography are of great interest to botanists. This study aims to investigate the phylogeny and biogeography of Cedrus based on sequence analyses of seven cytoplasmic DNA fragments.
The methods used were PCR amplification and sequencing of seven paternal cpDNA and maternal mtDNA fragments, parsimony and maximum likelihood analyses of the DNA dataset, and molecular clock estimate of divergence times of Cedrus species.
Phylogenies of Cedrus constructed from cpDNA, mtDNA and the combined cp- and mt-DNA dataset are identical in topology. It was found that the Himalayan cedar C. deodara diverged first, and then the North African species C. atlantica separated from the common ancestor of C. libani and C. brevifolia, two species from the eastern Mediterranean area. Molecular clock estimates suggest that the divergence between C. atlantica and the eastern Mediterranean clade at 23.49 +/- 3.55 to 18.81 +/- 1.25 Myr and the split between C. libani and C. brevifolia at 7.83 +/- 2.79 to 6.56 +/- 1.20 Myr.
The results, combined with palaeogeographical and palaeoecological information, indicate that Cedrus could have an origin in the high latitude area of Eurasia, and its present distribution might result from vicariance of southerly migrated populations during climatic oscillations in the Tertiary and further fragmentation and dispersal of these populations. It is very likely that Cedrus migrated into North Africa in the very late Tertiary, while its arrival in the Himalayas would not have been before the Miocene, after which the phased or fast uplift of the Tibetan plateau happened.
雪松属(真正的雪松)是一个非常重要的园艺植物类群。它在地中海地区和喜马拉雅山西部呈间断分布。其进化和生物地理学引起了植物学家的极大兴趣。本研究旨在基于七个细胞质DNA片段的序列分析来探究雪松属的系统发育和生物地理学。
所采用的方法包括对七个父系叶绿体DNA和母系线粒体DNA片段进行PCR扩增和测序、对DNA数据集进行简约法和最大似然法分析以及对雪松属物种的分歧时间进行分子钟估计。
由叶绿体DNA、线粒体DNA以及叶绿体-线粒体DNA联合数据集构建的雪松属系统发育树在拓扑结构上是相同的。结果发现,喜马拉雅雪松(Cedrus deodara)最先分化,然后北非物种大西洋雪松(Cedrus atlantica)从黎巴嫩雪松(Cedrus libani)和北非雪松(Cedrus brevifolia)(来自地中海东部地区的两个物种)的共同祖先中分离出来。分子钟估计表明,大西洋雪松与地中海东部类群之间的分歧时间为2349±355至1881±125万年前,黎巴嫩雪松和北非雪松之间的分歧时间为783±279至656±120万年前。
这些结果结合古地理和古生态信息表明,雪松属可能起源于欧亚大陆的高纬度地区,其目前的分布可能是由于第三纪气候振荡期间向南迁移的种群发生了隔离,以及这些种群进一步的碎片化和扩散。很可能雪松属在第三纪晚期迁移到了北非,而它到达喜马拉雅山的时间不会早于中新世,之后青藏高原发生了阶段性或快速隆升。