Abstract
Despite unparalleled access to species' genomes in our post-genomic age, we often lack adequate biological explanations for a major hallmark of the speciation process-genetic divergence. In the presence of gene flow, chromosomal rearrangements such as inversions are thought to promote divergence and facilitate speciation by suppressing recombination. Using a combination of genetic crosses, phenotyping of a trait underlying ecological isolation, and population genetic analysis of wild populations, we set out to determine whether evidence supports a role for recombination suppressors during speciation between the Z and E strains of European corn borer moth (Ostrinia nubilalis). Our results are consistent with the presence of an inversion that has contributed to accumulation of ecologically adaptive alleles and genetic differentiation across roughly 20% of the Ostrinia sex chromosome (~4 Mb). Patterns in Ostrinia suggest that chromosomal divergence may involve two separate phases-one driving its transient origin through local adaptation and one determining its stable persistence through differential introgression. As the evolutionary rate of rearrangements in lepidopteran genomes appears to be one of the fastest among eukaryotes, structural mutations may have had a disproportionate role during adaptive divergence and speciation in Ostrinia and in other moths and butterflies.