Monarch butterfly morphology, range expansion, and migration

A study suggests how range expansion and migration loss influence the evolution of monarch butterfly wings. Migration has evolved repeatedly to enable organisms to exploit seasonal variations in resource availability. How migration-associated traits evolve remains unclear, particularly after loss of migration. To better understand the evolutionary relationship between migration and migration-related traits, Micah Freedman and colleagues examined more than 6,000 museum specimens of monarch butterflies (Danaus plexippus) dating back to the mid-19th century. From their ancestral range in North America, monarchs have expanded across the Atlantic and Pacific Oceans during the past two centuries, and the expanded populations no longer migrate. Museum specimens representing the early stages of range expansions had larger and more elongated forewings than North American specimens. Specimens from Atlantic and Pacific locations exhibited significant decreases in forewing size and elongation over time, in contrast to specimens from either North America or from long-established nonmigratory populations in Central and South America or the Caribbean. Additionally, garden-reared, nonmigratory monarchs from Hawaii, Guam, Australia, and Puerto Rico had significantly smaller wings than North American migratory monarchs. The results suggest that migration-associated traits, such as large and elongated forewings, may be beneficial during initial range expansion, but not after the loss of migration, according to the authors.

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Article #20-01283:


“Two centuries of monarch butterfly collections reveal contrasting effects of range expansion and migration loss on wing traits,” by Micah G. Freedman, Hugh Dingle, Sharon Y. Strauss, and Santiago R. Ramírez.

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Micah G. Freedman

University of California

Davis, CA

tel: 864-506-1906

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