Fueling Long Distance Monarch Migration

Transcontinental-scale migrations (1000s km) of flying insects like the monarch butterfly (Danaus plexippus) are exemplars of physical endurance and fuel efficiency. Increasingly, anthropogenic factors like pesticides, land use, and climatic changes interfere with the strategies used to fuel their migratory cycle. One poorly understood aspect of insect migration is where they acquire the energy for fatty acid synthesis, which is required to fuel back-and- forth migratory movement (burning) and to meet ongoing physiological needs (e.g., navigation, feeding, decision-making). Understanding the spatial origins of energy from dietary sources for fatty acids synthesis along a migratory route to support long-distance migration and overwintering is crucial to the conservation of monarchs. Until now, no viable means for tracing the origins of fats in any insects were possible. In this study, we hypothesize that the spatial origins of essential (only accessible in the larval stage) and non-essential fatty acids in resident, migrating, and overwintering monarch butterflies in North America can be spatially quantified by using deuterium and carbon-13 isotope analyses of fatty acid molecules and wing chitin. We will use stable-isotope isotope analyses of essential and non-essential fatty acids on captive and wild samples of monarchs (abdomen, wings, head), larvae (body), and the host plants (Asclepias syriaca) of resident individuals. These expected stable-isotopic relationships obtained will be used to create continental fuel source maps to infer the origins and utilization of fatty acids in migrating and overwintering individuals. This project advances new biochemical analysis of component-specific stable-hydrogen and - carbon isotope ratios to unravel aspects of animal migration ecology previously intractable with conventional approaches like mark-and-recapture. Fatty acid stable-isotope analyses are anticipated to provide a foundational basis for mapping the origins of lipid resources and thereby reveal where resources are most needed to ensure long-term conservation goals. Results from this project will apply to other migratory insects and other species like birds. This project is a collaborative effort with Austria, Canada, Mexico, and the USA.