Resource Availability Modulates Gene Expression Across Life Stages in a Migratory Butterfly.

Natural populations are in constant need of balancing resource allocation to compensate for seasonal environmental variation. In many insects, a well-established trade-off between migration and reproduction exists. While this trade-off has been characterised phenotypically for decades, the underlying regulatory pathways are poorly understood. Here, we examined how resource-related environmental cues shape transcription across development in the long-distance migrant butterfly Vanessa cardui. In a multi-cue, developmental stage-specific design, adult females were exposed to host-plant presence or absence, while larvae experienced food limitation or crowding. Adult exposure to host plants was associated with differential expression in ecdysteroid and juvenile-hormone pathways, consistent with endocrine regulation of reproductive readiness and predictions of the oogenesis-flight syndrome. Larval resource limitation altered developmental and metabolic pathways, suggesting molecular predispositions and potential carry-over effects to adult traits. Across all contrasts, metabolism emerged as a shared axis linking responses across life stages. Together, our results show that resource-driven cues leave both stage-specific and general transcriptional signatures that connect environmental context with the molecular basis of migratory behaviour.