Abstract
INTRODUCTION: Invasive species pose a major threat to global biodiversity and agricultural productivity, yet the genomic mechanisms driving their rapid expansion into new habitats are not fully understood. The fall armyworm, Spodoptera frugiperda, originally from the Americas, has expanded its reach across the Old World, causing substantial reduction in crop yield. Although the hybridization between two genetically distinct strains has been well-documented, the role of such hybridization in enhancing the species' invasive capabilities remains largely unexplored. OBJECTIVES: This study aims to investigate the contributions of hybridization and natural selection to the rapid invasion of the fall armyworm. METHODS: We analyzed the whole-genome resequencing data from 432 individuals spanning its global distribution. We identified the genomic signatures of selection associated with invasion and explored their linkage with the Tpi gene indicating strain differentiation. Furthermore, we detected signatures of balancing selection in native populations for candidate genes that underwent selective sweeps during the invasion process. RESULTS: Our analysis revealed pronounced genomic differentiation between native and invasive populations. Invasive populations displayed a uniform genomic structure distinctly different from that of native populations, indicating hybridization between the strains during invasion. This hybridization likely contributes to maintaining high genetic diversity in invasive regions, which is crucial for survival and adaptation. Additionally, polymorphisms on genes under selection during invasion were possibly preserved through balancing selection in their native environments. CONCLUSION: Our findings reveal the genomic basis of the fall armyworm's successful invasion and rapid adaptation to new environments, highlighting the important role of hybridization in the dynamics of invasive species.