Use of essential versus nonessential fatty acids during flight in monarch butterflies: Implications for the importance of nectaring during migration

Abstract

Many insect species are migratory, but migration is energetically costly, leading to a trade-off between migration and subsequent reproduction. Of importance to the allocation of resources to migration and reproduction is the relative use of essential and nonessential fatty acids. How different ecological conditions experienced by individuals affect differential allocation of nutrients has not been well explored, especially in insects. Our goal was to evaluate how reproductive (summer) and migratory (fall) rearing conditions affect the source and allocation patterns of fatty acids used during experimental flights (0–6 h) in monarch butterflies (Danaus plexippus L.). We used larval and adult diets manipulated isotopically (δ¹³C) and chromatographic analyses to determine fatty acid composition and source in the fat body. C4 versus C3 carbohydrate feeding increased the δ¹³C value of lipids in monarchs (−31.2‰ vs. −22.1‰) and increased total fatty acid concentrations reflecting lipid synthesis during adult feeding. Fuel use during flight differed, with essential fatty acids being more conserved in fall versus summer conditions (21% vs. 32% loss, respectively), indicating that the environmental cues responsible for the onset of migration result in physiological changes that modify lipid use. Frequency of stopovers for nectar and nectar quality available during migration will influence the capacity of monarchs to conserve essential fatty acids up to and through the migration and overwintering period.