Hybridization-driven genomic plasticity enhances the global invasion of fall armyworm

The fall armyworm (FAW), Spodoptera frugiperda (J.E. Smith) (Lepidoptera: Noctuidae), is a highly migratory and polyphagous pest native to the Western Hemisphere and has recently invaded the Eastern Hemisphere with strong long-distance flight performance. In China, the FAW was first reported in Yunnan Province in January 2019 and has since spread throughout the country, posing a significant economic threat to China’s crop production.1 FAW populations in the Western Hemisphere are generally classified into two genetically distinct but morphologically indistinguishable strains, the “rice” and “corn” strains, which differ in host plant preferences and certain physiological traits.2 Since its discovery outside of the Americas in 2016, this species has rapidly expanded throughout Africa, Asia, and beyond, thanks in large part to hybridization-driven genetic flexibility, according to recent studies. It was discovered that the invasive populations in the Eastern Hemisphere were hybrids of the rice and corn strains, with a predominantly corn-strain nuclear genetic background.3 Although the invasive mechanism of FAW has been widely explored, the specific contribution of hybridization to its invasive potential and adaptive capacity remains poorly understood. This paper mainly examines three key trends: (1) the role of hybridization in maintaining genetic diversity, (2) genomic signatures of selection linked to environmental adaptation in invaded regions, and (3) phenotypic divergence mediated by hybridization. Together, these factors help explain the high invasive potential of FAWs in both their native and newly invaded habitats.

Hybridization enhances genetic diversity and facilitates rapid adaptation

Global population genomics analyses have confirmed the American origin of FAW and revealed an invasion pathway characterized by rapid dispersal into Asia via Africa as a bridgehead (accession number: PRJNA591441) (Figure 1A).3 Invasive populations in the Eastern Hemisphere have undergone extensive interstrain hybridization, introducing novel nuclear genetic variation. Consequently, these populations exhibit significantly higher levels of genomic diversity compared to their native Western Hemisphere counterparts (p < 0.0001) (Figure 1B).4 Moreover, the invasive populations exhibit distinct genetic structures and relatively low intra-regional differentiation, suggesting rapid evolutionary change post-introduction.3,4 Importantly, these invasive populations are not derived from a single introduction event. Instead, they reflect a complex invasion scenario involving multiple introductions followed by genetic admixture. Many individuals from Asia and Africa carry hybrid genotypes, indicating widespread interstrain hybridization after arrival. This hybridization likely enhanced the species’ adaptive potential, facilitating its successful establishment and rapid expansion in novel environments.