Local Genetic Signatures of a Global Weed: Population Structure and Ecological Drivers of Capsella bursa-pastoris Diversity in the Korean Peninsula

Abstract

Genetic variation in widespread plant species is shaped by adaptation to local environments and gene flow among subpopulations. Capsella bursa-pastoris is a globally distributed weedy species and a model for studying polyploid genome evolution. The demographic history of European populations has been well characterized, yet East Asian populations of C. bursa-pastoris are poorly explored. Here, we use RADseq data to investigate the genetic diversity and population structure of 187 C. bursa-pastoris accessions across the Korean Peninsula, a region of mountainous terrain and extensive ecological heterogeneity. In contrast to European populations, which show high rates of selfing, we found that Korean populations exhibited signs of outcrossing, potentially resulting from high population density influenced by human activities embedded in Korean history and culture. Widespread genetic admixture contributed to the overall low genetic differentiation, as multiple introgression events into Korea may have occurred, followed by extensive gene flow among populations mediated by human activities. The genetic differentiation that was detected was largely correlated with geographic and climatic divergence. Taken together, our findings highlight the potential for range expansions to be accompanied by shifts in mating systems and suggest that Korean C. bursa-pastoris populations provide an ecological model for studying the transition from selfing to outcrossing.