Hypothesis: Different generations of a seasonally polyphenic butterfly allocate their resources differently between dispersal ability and reproduction to fit the environmental circumstances specific to the seasonal environment of each generation.

Organism: Map butterfly (Araschnia levana).

Site of experiments: The Department of Zoology/Tovetorp Research Station, Stockholm University.

Methods: We estimated fecundity by assessing the amount of the limiting resource nitrogen that individuals of each generation allocated to their abdomens. We studied dispersal ability by assessing thorax nitrogen content, and by studying flight ability of both generations in a suite of temperatures.

Results: Individuals of the summer generation performed longer sustained flights than individuals of the spring generation in all temperatures except the warmest treatment. In males, abdomen nitrogen content was poorly correlated with thorax nitrogen content. Thus males do not need to trade off nitrogen between the tissues. However, female thorax and abdomen nitrogen contents were strongly positively correlated, and although summer females were better flyers than spring females, they still allocated disproportionately more nitrogen to the reproductive tissue in the abdomen. We conclude that the divergent allocation patterns between different Map butterfly generations are better understood in terms of developmental constraints acting on spring butterflies, rather than by season-specific adaptations.