Phylogeography of East Asian Lespedeza buergeri (Fabaceae) based on chloroplast and nuclear ribosomal DNA sequence variations

초록

The dynamic changes in land configuration during the Quaternary that accompanied by climatic oscillations have significantly influenced to current distribution and genetic structure of East Asian warm-temperate forests. Although recent surveys have testified this hypothesis, more cases are still demanded, including Korean Peninsula. Thus, determining their genetic structure is a major task that will help us understand the migration history of extant populations and obtain taxonomic and systematic insight. We inferred the structure of Lespedeza buergeri, a warm-temperate shrub that is disjunctively distributed around the East China Sea (ECS) at the southern tip of Korea, China, and Japan. Two non-coding regions (rpl32-trnL, psbA-trnH) of chloroplast DNA (cpDNA) and internal transcribed spacer of nuclear ribosomal DNA (nrITS) were analyzed for 188 individuals from 16 populations. The nrITS data revealed a clear phylogeographical structure (NST > GST; 0.762 vs. 0.460), and roughly two geographical clades (China vs. Korea and Japan), plus subclades within Japan. However, we found no strongly supported distinct groups based on cpDNA data. These results indicate frequent migration by this species via an ECS land bridge during the early Pleistocene that then tapered gradually beginning in the middle Pleistocene. We hypothesize that the current distribution of L. buergeri is overall approximate to vicariance of a widely occurring species for which movement was initially inhibited by a strengthened ECS barrier. Despite of vicariance, we proposed a possibility of hybridization origin of plants in the Korean populations sampled here based on genetic and morphological evidences.