Genetic variation and population differentiation of Michelia formosana (Magnoliaceae) based on cpDNA variation and RAPD fingerprints: relevance to post-Pleistocene recolonization |
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Authors: | S-Y Lu K-H Hong S-L Liu Y-P Cheng W-L Wu T-Y Chiang |
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Institution: | (1) Division of Forest Biology, Taiwan Forestry Research Institute, Taipei, Taiwan, TW;(2) Department of Biology, Cheng-Kung University, Tainan 701, Taiwan e-mail: tychiang@mail.ncku.edu.tw, TW |
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Abstract: | We used sequence variation of the atpB-rbcL intergenic spacer of cpDNA and nested clade analysis to assess the phylogeographic pattern of Michelia formosana, a species restricted to Taiwan and the Ryukyus. In total, 31 haplotypes were identified and clustered into four major chlorotypes.
Genetic composition of nearly all populations was heterogeneous and paraphyletic phylogenetically. Although the apportionment
of cpDNA variation hardly revealed a geographic pattern due to the coancestry of dominant sequences, some chlorotypes were
restrictedly distributed. According to the patterns of clade dispersion and displacement, a reconstructed minimum spanning
network revealed that historical events of past fragmentation and range expansion, associated with glaciation, may have shaped
the phylogeographic patterns of M. formosana. Four possible refugia were identified: the Iriomote and Ishigaki Islands (the southern Ryukyus), Wulai (northern Taiwan),
and Nanjen (southern Taiwan), on the basis of the interior positions of their haplotypes in the network and the high level
of nucleotide diversity. Given insufficient time for coalescence at the cpDNA locus since the late Pleistocene recolonization,
lineage sorting led to low levels of genetic differentiation among populations. In contrast, hierarchical examination of the
random amplified polymorphic DNA (RAPD) data scored from six populations across three geographical regions, using an analysis
of molecular variance (AMOVA), indicated high genetic differentiation both among populations (ΦST = 0.471) and among regions (ΦCT = 0.368). An unweighted pair group method with arithmetic mean (UPGMA) tree of the RAPD fingerprints revealed that populations
of two offshore islands of eastern Taiwan (M. formosana var. kotoensis) were clustered with geographically remote populations of the Ryukyus instead of those in southern Taiwan, suggesting some
historical division due to geographic barriers of the central mountain range. In contrast to the paraphyly of the nearly neutral
cpDNA alleles, differentiated RAPDs may have experienced diversifying selection.
Received: July 2, 2001 / Accepted: February 20, 2002 |
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Keywords: | atpB-rbcL noncoding spacer cpDNA Michelia formosana Minimum spanning network Phylogeography RAPD |
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