Patterns of genomic and allochronic strain divergence in the fall armyworm, Spodoptera frugiperda

Speciation is the process through which reproductive isolation develops between distinct populations. Because this process takes time, speciation studies often necessarily examine populations within a species that are at various stages of divergence. The fall armyworm, Spodoptera frugiperda (J.E.Smith), is comprised of two strains (R=Rice & C=Corn) that serve as a novel system to explore population divergence in sympatry. Here, we use ddRADSeq data to show that fall armyworm strains in the field are largely genetically distinct, but some interstrain hybridization occurs. Although we detected F1 hybrids of both R- and C-strain maternal origin, only hybrids with R-strain mtDNA were found to contribute to subsequent generations, possibly indicating a unidirectional barrier to gene flow. Although these strains have been previously defined as ‘host plant-associated,’ we recovered an equal proportion of R- and C-strain individuals in fields dominated by C-strain host plants. As an alterna..., ,