Repeated origin of the W chromosome from the Z chromosome in Lepidoptera

Abstract We built a chromosome-level genome assembly of the Asian corn borer, Ostrinia furnacalis Guenée (Lepidoptera: Pyralidae, Pyraloidea), an economically important pest in corn, from a female, including both the Z and W chromosome. Despite deep conservation of the Z chromosome across Lepidoptera, our chromosome-level W assembly reveals this chromosome has recently derived from the O. furnicalis Z chromosome. We also recover evidence for convergent formation of the W in two other related families, all independently derived from the Z chromosome. Despite its recent origin, the W chromosome has accumulated significant repetitive elements and experienced rapid pseudogenization, illustrating that degeneration can occur rapidly following recombination suppression. Our results, taken together, reveal remarkable dynamics for the sex chromosomes in this otherwise highly-conserved clade.