| Summary: | 博士 === 國立臺灣師範大學 === 生物研究所 === 90 === Population and geographic structure of Miscanthus condensatus, a clonal grass distributed along the coasts of Japan, Ryukyu and Taiwan Islands, was estimated based on random amplified polymorphic DNA (RAPD) fingerprints, nucleotide variation of the nuclear alcohol dehydrogenase 1 locus, atpB-rbcL intergenic spacer of cpDNA and trnD-trnT spacer of mtDNA. RAPD fingerprinting revealed significant differentiation among populations. Like many inbreeding species, low levels of nucleotide diversity were detected at all nuclear and organelle loci. The likely phylogeographic pattern of M. condensatus, as reflected by the correlation between population differentiation values based on the cpDNA variation and geographic distance, represents isolation between north and south Kerama gap since the mid-Pleistocene. The phytogeographic pattern shown in the reconstructed network and nested clade analysis suggests that the present-day M. condensatus populations in the Pacific island arcs from Japan to Taiwan were derived from ancestral populations with multi-haplotypes in continental Asia, which migrated to the island via land bridge and super-island. Given small number of colonists and infrequent gene flow, genetic drift would result in among-population heterogeneity and within-population homogeneity. Significantly negative Tajima’s S statistics were detected in overall exons and replacement sites of the Adh 1 locus, agreeing with the demographic expansion hypothesis. Pairwise comparisons of the Ka/Ks ratio at the Adh 1 locus revealed that lineages linking closely related populations of the species appeared to be under Darwinian positive selection.
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