Making Monarch Migrants: Evaluation of flight energetics, wing morphology, and egg development

The Monarch butterfly (Danaus plexippus) is an iconic insect species with a complex, migratory life-history that spans most of North America. Seasonal environmental changes in photoperiod and temperature are well-known drivers of phenotypic differences between fall and summer monarch populations, such as wing morphology and reproductive development, but little is known about the energetic costs of flight, what factors influence flight success and efficiency, and how migratory and non-migratory generations differ. To begin addressing these questions, we conducted a controlled laboratory experiment in which monarchs were raised from egg in two separate growing conditions to induce phenotypic expressions of migrants and non-migrants. One treatment chamber was set to mimic fall-like conditions with a daily decreasing photoperiod and temperature and another chamber was set to mimic summer-like conditions with a constant photoperiod and temperature. Upon eclosion, we recorded adult wing lengths, number of mature and immature oocytes in females, and evaluated in-flight energetics using flow-through respirometry on both sexes. By comparing results from summer- and fall-reared monarchs we can better assess how various stressors, nutrients and resources influence monarch migration and physiological development.