AOBPreview originally published online on July 4, 2007
Annals of Botany 2007 100(3):573-580; doi:10.1093/aob/mcm134
Phylogeny and Biogeography of Cedrus (Pinaceae) Inferred from Sequences of Seven Paternal Chloroplast and Maternal Mitochondrial DNA Regions
1 State Key Laboratory of Systematic and Evolutionary Botany, Institute of Botany, The Chinese Academy of Sciences, Beijing 100093, China
2 Graduate School of the Chinese Academy of Sciences, Beijing 100039, China
* For correspondence. E-mail xiaoq_wang{at}ibcas.ac.cn
Received: 24 December 2006 Returned for revision: 16 March 2007 Accepted: 23 May 2007 Published electronically: 4 July 2007
Background and Aims 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.
Methods: 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.
Key Results: 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.
Conclusions: 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.
Key words: Cedrus, molecular phylogeny, biogeography, Mediterranean, Himalayas, molecular clock
These authors contributed equally to the work.