High-quality reference genomes of swallowtail butterflies provide insights into their coloration evolution

Swallowtail butterflies (Papilionidae) are a historically significant butterfly group due to their colorful wing patterns, extensive morphological diversity, and phylogenetically important position as a sister group to all other butterflies and have been widely studied regarding ecological adaption, phylogeny, genetics, and evolution. Notably, they contain a unique class of pigments, i.e., papiliochromes, which contribute to their color diversity and various biological functions such as predator avoidance and mate preference. To date, however, the genomic and genetic basis of their color diversity and papiliochrome origin in a phylogenetic and evolutionary context remain largely unknown. Here, we obtained high-quality reference genomes of 11 swallowtail butterfly species covering all tribes of Papilioninae and Parnassiinae using long-read sequencing technology. Combined with previously published butterfly genomes, we obtained robust phylogenetic relationships among tribes, overcoming the challenges of incomplete lineage sorting (ILS) and gene flow. Comprehensive genomic analyses indicated that the evolution of Papilionidae-specific conserved non-exonic elements (PSCNEs) and transcription factor binding sites (TFBSs) of patterning and transporter/cofactor genes, together with the rapid evolution of transporters/cofactors, likely promoted the origin and evolution of papiliochromes. These findings not only provide novel insights into the genomic basis of color diversity, especially papiliochrome origin in swallowtail butterflies, but also provide important data resources for exploring the evolution, ecology, and conservation of butterflies.