Population genetics of monarchs around the world
Monarchs are well known for their annual migration from eastern North America to overwintering sites in Mexico, but they also occur in western North America, where they overwinter along the Californian coast. Furthermore, monarchs form non-migratory populations around the world, ranging from locations in New Zealand to Costa Rica and Spain. Although these different populations have been known for a long time, it remained unknown how monarchs spread around the world and whether monarchs in different populations are genetically different. We addressed these questions using multiple techniques, including whole-genome sequencing. Surprisingly, this work showed that monarchs originate in North America, and that they subsequently colonized the world through independent dispersal events across the Atlantic Ocean, across Central and South America, and across the Atlantic Ocean. During these dispersal events, monarchs formed genetically distinct populations and lost their migration. Another surprising finding was that monarchs in eastern and western North America, despite their drastically different migration destinations and distances, do not show genetic differentiation, suggesting that their differences in migration are driven by gene expression.
- How much gene flow occurs between different populations of monarchs?
- Has genetic differentiation between monarch populations contributed to local adaptation?
- Are there specific genomic regions that show strong genetic differentiation between migratory monarchs with different migration distances and destinations?