Insights from Chloroplast DNA into the Progenitor-Derivative Relationship Between Campanula punctata and C. takesimana (Campanulaceae) in Korea

Of the nearly 40 endemics present on Ulleung Island, Campanula takesimana Nakai represents an anagenetically derived lineage of a continental progenitor, C. punctata Lam. Other than its low morphological divergence, little is known about the genetic diversity and population structure of the species pair or the geographical origin of C. takesimana. We sampled a total of 240 accessions in 22 populations, including one Dokdo Island population, of the two species, sequenced four noncoding chloroplast regions (rps16-trnK, trnQ-rps16, psbD-trnT, and psbM-trnD; 4482 bp), and assessed the genetic consequences of anagenetic speciation. Based on chloroplast DNA, we found substantially lower genetic diversity statistics for C. takesimana compared to its progenitor, significant population genetic structuring in insular derivative species, and significant molecular divergence between C. punctata and C. takesimana. Mutually exclusive haplotypes were found in the two species, and the haplotype network suggested that Ulleung Island haplotypes were derived from the Dokdo Island haplotype, which was originally derived from a C. punctata population in Bonghwa-gun, Gyeongsangbuk-do Province. This study pinpoints a very narrow geographical source area and suggests the potentially important role of Dokdo Island as an initial stepping stone for Ulleung Island endemics.