Gene expression responses to environmental cues shed light on components of the migratory syndrome in butterflies

Migration is a complex behavior involving the synchronisation of many physiological and behavioral processes. Environmental cues must thus be interpreted to make decisions regarding resource allocation between, for example, migration or reproduction. In butterflies, the lack of host plants to sustain a new generation may indicate the need to migrate. Here, we used the painted lady butterfly ( Vanessa cardui ) as a model to characterize gene expression variation in response to host plant availability. Assessment of the response to host plant availability in adult female butterflies revealed significant modifications in gene expression, particularly within hormonal pathways (ecdysone oxidase and juvenile hormone esterase). We therefore hypothesize that tuning the ecdysone pathway may play a crucial role in regulating the timing of migration and reproduction in adult female painted lady butterflies. In addition, our analysis revealed significant enrichment of genes associated with lipid, carbohydrate, and vitamin biosynthesis, as well as the immune response. As environmental acquisition occurs throughout the life cycle, we also tracked gene expression responses to two other environmental cues across major developmental stages. Differences in both larval crowding and host plant availability during development resulted in significant changes in the expression of genes involved in development, reproduction and metabolism, particularly at the instar V larval stage. In summary, our results offer novel insights into how environmental cues affect expression profiles in migratory insects and highlight candidate genes that may underpin the migratory syndrome in the painted lady butterfly.