Food stress sensitivity and flight performance across phosphoglucose isomerase enzyme genotypes in the sooty copper butterfly

Interest in genetic variation at allozyme loci, especially at phosphoglucose isomerase (PGI), has considerably increased over recent decades. In this study, we investigated variation in food stress sensitivity and flight performance, two traits closely linked to individual fitness, across PGI genotypes in the sooty copper butterfly Lycaena tityrus. PGI genotype significantly affected growth rate and pupal mass, but had no overall effect on development time or flight performance. A significant genotype × sex × feeding treatment interaction showed that females from the rarest genotypes showed the strongest increase in development time under food stress. At the same time, these females exhibited the weakest reduction in body mass compared to non food-stressed individuals, while the most common PGI genotypes showed the highest reduction (significant interaction between genotype and feeding treatment). Such results suggest that effects of food stress on pupal mass may not pose a particularly strong selective pressure in L. tityrus. Generally, sex-specific differences in and effects of food stress on life-history traits were as expected, with, e.g., males showing a more rapid development, lower pupal mass and better flight performance than females.