The monarch butterfly (Danaus plexippus) is known for its annual long-distance migration from southern Canada to Michoacán, Mexico, where the species over-winters in reproductive diapause. Migratory species often have significant impacts on ecosystem processes by transferring nutrients between ecosystems and altering food web dynamics. Tropical milkweed (Asclepias curassavica) is commonly planted along the Gulf Coast, an area where the plant is not native. The plant-insect interactions of different milkweed species and monarchs is a large area of research, some of which addresses whether the phenology of A. curassavica may disrupt monarch migration or reduce fitness via OE (Ophryocystis elektroscirrha) spore accumulation. In this study, we look at the impact of diets of different milkweed species on quantitative morphological characteristics in adult monarch butterflies. Monarch caterpillars were raised on diets of native milkweed Asclepias incarnata (N = 20) and tropical milkweed A. curassavica (N = 20). Within 24 hours of emergence from the chrysalis, monarch adults were harvested for wings. Wings were processed into standardized images using a flatbed scanner. Images of wings were analyzed for wing area, wing length, and hue of wing coloration using ImageJ.
Results/Conclusions
Preliminary results indicate that different diet treatments have an effect on monarch morphology, both in males and females. We found that monarchs on diets of native milkweed had larger wings and deeper wing hues than monarchs on diets of non-native milkweed. We believe that higher levels of cardenolides in non-native milkweed compared to native milkweed may cause a metabolic tradeoff for investment in wing size and wing hue. By appropriating metabolic resources to sequestering higher levels of cardenolide toxins, monarchs on a diet of non-native milkweed invest less resources into increasing wing size and deepening wing hue. Wing morphology has potential implications on migration fitness and sexual selection. These results contribute some understanding important to the bigger issue of whether or not the widespread planting of A. curassaivica along the Gulf Coast is negatively impacting the migratory fitness of monarch butterflies.