Data availability
The sequencing reads have been submitted to European Nucleotide Archive (ENA) with the project accession number PRJEB33413. The scripts used for the genomic analysis can be found at https://github.com/venta380/Monarch_genomics. Flight, wing morphology and gene expression data have been uploaded to Dryad Digital Repository, doi:10.5061/dryad.hh4j1f6.