Dispersal and migration have contrasting effects on butterfly flight morphology and reproduction

Movement may fundamentally alter morphology and reproductive states in
insects. In long-distance migrants, reproductive diapause is associated
with trade-offs between diverse life history traits such as flight
morphology and lifespan. However, many non-diapausing insects engage in
shorter resource-driven dispersals. How diapause and other reproductive
states alter flight morphology in migrating versus dispersing insects is
poorly understood. To find out, we compared flight morphology in different
reproductive states of multiple butterfly species. We found that
dispersers consisted of ovulating females with higher egg-loads compared
to non-dispersing females. This trend was in stark contrast to that of
migrating female butterflies in reproductive diapause that made
substantially higher investment in flight tissue compared to
reproductively active, non-migrating females. Thus, long-distance
migration and shorter resource-driven dispersals had contrasting effects
on flight morphology and egg-loads. In contrast, male flight morphology
was not affected by dispersal, migration, or associated reproductive
states. Thus, dispersal and migration affected resource allocation in
flight and reproductive tissue in a sex-specific manner across relatively
mobile versus non-dispersing individuals of different species. These
findings suggest that dispersals between fragmented habitats may put extra
stress on egg-carrying females by increasing their flight burdens.