Female butterflies modulate investment in reproduction and flight in response to monsoon-driven migrations

Migratory species may display striking phenotypic plasticity during individual lifetimes. This may include differential investment in body parts and functions, differential resource use and allocation, and behavioural changes between migratory and non-migratory phases. While migration-related phenotypic changes are well-reported, their underlying mechanisms are usually poorly understood. Here we compare individuals from migratory (reproductive diapause) and non-migratory (reproductive) phases of closely related aposematic butterfly species to study how sexual dimorphism and migratory behaviour underlie significant morphological tradeoffs, and propose a plausible scenario to explain the migration-related phenotypic plasticity observed in females of migratory species. We found that female butterflies invested significantly more in their abdominal mass compared to males irrespective of their migratory phase, and underwent a clear shift in their body mass allocation after the switch from th...