Genetic homogenization in introduced Ambrosia artemisiifolia populations driven by pollen-mediated gene flow: Implications for its control strategies in China

Clarifying the processes that shape genetic patterns in invasive species requires disentangling introduction history from contemporary gene flow, which is crucial for uncovering invasion mechanisms and guiding management strategies. This challenge can be addressed by comparing maternally and biparentally inherited markers to isolate the signal of historical seed dispersal in chloroplast DNA from the combined influence of pollen and seed flow in nuclear data. In this study, we employed chloroplast sequences and nuclear microsatellite markers across 16 populations of Ambrosia artemisiifolia in China to reconstruct its invasion history and estimate ongoing gene flow. Genetic analyses revealed high within-population diversity and an absence of bottlenecks, consistent with the consequences of multiple introductions. Three previously documented introduction epicenters were confirmed, including Siping–Tieling–Shenyang, Nanjing, and Nanchang-Jiujiang. The strong discordance in population differentiation between chloroplast and nuclear markers (FST = 0.634 vs 0.113) indicates that contemporary pollen-mediated gene flow (pollen/seed flow ratio = 15.080) might be the dominant factor responsible for the genetic homogenization across Chinese invasive range, particularly in southern China. Our results indicate that the genetic pattern of high diversity but low differentiation in invasive A. artemisiifolia is not due to introductions from a pre-admixed source but is overwhelmingly shaped by contemporary pollen-mediated gene flow. These findings provide a mechanistic understanding of invasion dynamics and underscore the need to manage both historical source regions and ongoing pollen dispersal for effective control.