Seasonal butterfly design: morphological plasticity among three developmental pathways relative to sex, flight and thermoregulation

The temperate-zone butterfly Pararge aegeria can use three developmental pathways corresponding to different seasonal cohorts: (1) development with a pupal winter diapause resulting in early spring adults; (2) development with a larval winter diapause resulting in late-spring adults and (3) direct development resulting in summer or second generation adults. In order to test adaptive predictions, we compared variation in flight- and thermoregulation-related morphology among adult males and females from the three pathways using both field data (i.e. wild-caught butterflies) and experimental breeding data (i.e. reared under different photoperiod regimes). Morphological patterns among the pathways were largely similar in the field and rearing data. Seasonal patterns differed between the sexes for most traits, including (relative) size measures and wing colour. Our results suggest sex-related, adaptive seasonal plasticity for morphological traits related to flight behaviour in a multivoltine insect.