Cpdna Phylogeographic Study Of Cercidiphyllum Sieb. Et Zucc

Cercidiphyllum Sieb. et Zucc, the sole representative of the monotypic family Cercidiphyllaceae, has been considered to be a primitive, relictual angiosperm. The genus is well represented in the fossil record with occurrences in the late Cretaceous and Tertiary of North America and Europe, but it is now confined to East Asia. Cercidiphyllum contains two extant species, Cercidiphyllum japonicum Sieb. et Zucc. and C. magnificum Nakai. Populations of C. japonicum are disjunct between East China and Japan, but C. magnificum is native to central Honshu of Japan where it grows at higher altitudes than C. japonicum. To infer historical processes (vicariance and/or dispersal), detect gene flow among populations, and clarify the origin of an endemic species in Japan (C. magnificum), we studied on the population genetics and phylogeography of Cercidiphyllum using four non-coding region fragment of cpDNA. The main results are summarized as follows:After a preliminary survey on 25 chloroplast DNA fragments, we obtained 4 phylomophic fragments (petA-psbJ, psbE-petL, rpL32-trnL, F71-R1516 intergenetic spacers). Then we amplified and sequenced these 4 fragments for 247 individuals from 49 populations. Eighteen variation sites were detected and 12 cpDNA haplotypes were recovered. Cercidiphyllum japonicum and C. magnificum harboured a low relative level of genetic diversity in C. japonicum (nucleotide diversity:Pi= 0.35×10-3; haplotype diversity:h=0.784) and C. magnificum (Pi=0.15×10-3; h= 0.5). AMOVA analysis revealed most of the variation existed among populations in both C. magnificum (FST-0.566) and C. japonicum (FST=0.938). In C. japonicum, a hierarchical AMOVA indicated that 89.08% of variation occurred among three regions (Northern Japan, Southwestern Japan and Southern China, and Northern China). Genetic diversity and nested clade analysis revealed that Quaternary glacial refuges of Cercidiphyllum are located in the Mt. Emei region in western China, Mt. Hupingshan and Houhe area in central China, Nagano and Tochigi in central Japan. Based on phylogenetic analysis of haplotypes, populations of Cercidiphyllum differentiatied into two lineages [SJC-NC (southern Japan-China vs. the NJ (northern Japan)]. A coalescent-based model of'divergence by isolation with migration', support an ancient (Early-Pleistocene) divergence between two lineages. After that, the two lineages experienced different evlutionary history. The population expansion events, followed by serious fragementation and genetic drift may be responsible for the current geographic and genetic distribution patterns of SJC-NC lineage. The NJ lineage retreated to the refuge of central Honshou during the glacial period of late Quaternary, while during postglacial this lineage migrated northward.