Generations of the polyphenic butterfly Araschnia levana differ in body design

The European Map Butterfly, Araschnia levana (Nymphalidae), represents a classical example of seasonal polymorphism, in which summer and spring generations differ strikingly in wing colour pattern. Although the physiological background to the formation of the two forms is well known, few studies have explored its possible ecological significance. Based on previous findings that both population number and body size tend to be larger in summer, we examined the hypothesis that the summer generation is more capable of long-distance dispersal. We re-analysed mark–recapture data on the butterfly using the multi-strata modelling design in the program MARK, compared biomechanical design traits of the spring- and summer-generation butterflies using canonical variate analysis, and tested for inter-generation differences in allometry relations of design traits to body size. The summer butterflies had shorter residence times and a higher probability of movements among capture sites than the spring butterflies, indicating greater mobility. Regarding the design traits, adults of summer-generation butterflies had a heavier thorax, lower abdomen to body mass ratio, larger wing area, less pointed wings and lower wing loading. The differences in design trait