Genomic evidence for panmixia of eastern and western North American migratory monarch butterflies

Monarch butterflies are known for their spectacular annual migration in eastern North America, with millions of monarchs flying up to 4,500 kilometers to overwintering sites in central Mexico. Monarchs also live west of the Rocky Mountains, where they travel shorter distances to overwinter along the Pacific Coast. Monarch numbers have recently dwindled, and monarch migration may be on the brink of extinction. It is often assumed that eastern and western monarchs form distinct evolutionary units that require specific protection, but genomic studies to support this notion are lacking. We used a tethered flight mill to show that migratory eastern monarchs have greater flight performance than western monarchs. However, analyzing more than 20 million SNPs in 43 monarch genomes, we found no evidence for genomic differentiation between eastern and western monarchs, suggesting the existence of one panmictic migratory population. Our genomic analysis also showed identical and low levels of genet..., Talla_East_West_North_America_Monarch_Genomics_Flight_And_Wing_Morphology_DataFlight trial and wing morphology dataTalla_East_West_North_America_Monarch_Genomics_Gene_Expression_DataGene expression data,