Fig. 4

Origin of W chromosomes and formation of neo-W chromosome. A The simplified Phylogenetic Tree of Lepidoptera with Latin names painted in different colors represents species of different families. The black arrow represents Lepidoptera acquired ancestor W chromosome 143 million years ago. The red arrow represents P. bucephala formed neo-W chromosome through chromosome fusion with ancestral chromosome 21 within 56 million years. The green arrows represent the W chromosomes acquired in the Wolbachia bacterial genome through horizontal transfer. C. ligustri acquired the Wolbachia bacterial genome within 27 million years, L. populi acquired Wolbachia bacterial genome within 28 million years, and L. camilla acquired Wolbachia bacterial genome within 60 million years. B The 11 orthologs between P. bucephala W chromosome and P. bucephala Neo-Z chromosome. The orthologous relationships of two retrotransposons were marked with red. C The eight orthologs between P. bucephala W chromosome and ancestral chromosome 21. D Blue and red links indicate synteny blocks of the Wolbachia bacterial genome and the W chromosome of C. ligustri, in forward and reverse orientation, respectively