Many animals undergo long-distance seasonal migrations to escape deteriorating habitats, colonize new resources or escape natural enemies. Animal migration has major impacts on the ecology and evolution of migrating species as well as on ecosystem functioning. Despite the importance of animal migration, the genetics underlying this phenomenon remain poorly understood. This project will characterize the genetic architecture of seasonal migration, using monarch butterflies as a model system. Because many of the traits related to migration are shared with other species, this work will also greatly advance our general understanding of animal migration. There is also a pressing need to understand the genetics of monarch migration. The population size of eastern migratory monarchs has dwindled over the last few decades, and it has been suggested that this spectacular phenomenon may disappear in the near future. A thorough understanding of monarch migration genetics must be achieved in order to determine whether monarch migration is at risk of extinction, and whether non-migratory populations could potentially re-evolve migration to supplement the dwindling North American population. This project will also have a variety of broader impacts, including the training of students and post-doctoral researchers, and outreach activities at public schools, science centers, and monarch butterfly festivals. Seasonal migration occurs widely across the animal kingdom, but a comprehensive understanding of migration genetics is lacking for any species. Migration is not a single trait, but is better described as a syndrome that includes a variety of traits, including those involved in metabolism, development, sensory processing and reproduction. Monarch butterflies are well suited to study migration because of their naturally occurring variation in migratory phenotypes, and the growing availability of genetic tools in this species. Monarchs are best known for their spectacular annual migration in eastern North America, during which millions of monarchs fly from the US and Canada to overwintering sites in Mexico. What is less appreciated is that monarchs west of the Rocky Mountains undergo a shorter migration to the California coast, and that monarchs have formed non-migratory populations around the world. This project will capitalize on this naturally occurring variation in migration phenotypes to obtain a comprehensive view of the genetics of migration. To do this, the researchers will perform genetic crosses between migratory and non-migratory monarchs and quantify phenotypic traits related to migration in parental and F2 generations. They will re-sequence monarch genomes, perform Quantitative Trait Locus mapping and use targeted genome editing to: (1) identify genomic regions and genes associated with migration phenotypes; (2) characterize behavior and genetics associated with divergent migration distances; and (3) functionally test candidate migration genes. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.