Yun-Gyeong Choi1P, Watanabe Yoichi2, Sang-Hun Oh1

1Department of Biology, Daejeon University, Daejeon, Korea; 2Graduate School of Horticulture, Chiba University, Matsudo, Chiba, Japan

Island biodiversity often displays complex and unpredictable evolutionary patterns. Ulleung Island, a volcanic oceanic island located in the East Sea, is well known for its high level of endemic plant diversity. However, to fully understand the origins of biodiversity on Ulleung Island, it is also essential to investigate non-endemic taxa that are distributed both on the island and the mainland. Viburnum furcatum Blume ex Maxim. (Adoxaceae) is a representative non-endemic deciduous shrub found in temperate mountainous regions across Ulleung Island, Jeju Island, and Japan. In this study, we conducted Genotyping-by-Sequencing (GBS) on 95 individuals from 15 populations across Ulleung Island, Jeju Island, and Japan, generating a total of 102,656 SNP loci. Genetic diversity analysis revealed that the Ulleung population had the highest observed heterozygosity (0.215) and the lowest inbreeding coefficient (–0.087), indicating a genetically stable and independently structured population. STRUCTURE, PCA, and maximum likelihood (ML) phylogenetic analyses also showed that the Ulleung population formed a distinct genetic cluster, clearly separated from populations in Jeju and Japan. Pairwise FST values revealed strong genetic differentiation, with a maximum value of 0.781 between Ulleung and other regions. These results suggest that, despite being a non-endemic species, the Ulleung population of V. furcatum has diverged genetically due to geographic isolation. Although morphologically similar to conspecific populations, the Ulleung population exhibits clear genetic distinctiveness, indicating that cryptic divergence may be occurring within this island population.