Molecular evidence for hybrid origin of Aster chusanensis,an endemic species of Ulleungdo,Korea

Ulleungdo is a small volcanic island and harbors many endemic plant species. Aster chusanensis Lim et al., a recently discovered endemic species on the island was proposed to be derived from hybridization between A. pseudoglehnii Lim et al. and A. oharai Nakai. To test hybrid origin of A. chusanensis, we sequenced the nrITS and three non-coding regions of a plastid genome (trnL-F, rbcL-accD, and psbA-trnH) from eight accessions of A. chusanensis and 37 accessions of its putative parents. Extensive investigation of the genome of A. chusanensis using 160 nrITS PCR amplicon sequences confirmed co-occurrence of nrITS sequences of the parental species within all accessions sampled. The retention of intact parental nrITS types in the genomes of A. chusanensis suggests that hybrid speciation has occurred recently on the island. The plastid DNA sequence data indicate that all of the hybrid individuals inherit the plastid from A. pseudoglehnii, except for one, which has the plastid of A. oharai, implying bidirectional but highly biased hybridization events during the evolution of A. chusanensis. Results of this study suggest that hybridization is an important process in the diversification of indigenous plants on Ulleungdo.