Significant effects of Pgi genotype and body reserves on lifespan in the Glanville fritillary butterfly

Individuals with a particular variant of the gene phosphoglucose isomerase ( Pgi ) have been shown to have superior dispersal capacity and fecundity in the Glanville fritillary butterfly ( Melitaea cinxia ), raising questions about the mechanisms that maintain polymorphism in this gene in the field. Here, we investigate how variation in the Pgi genotype affects female and male life history under controlled conditions. The most striking effect is the longer lifespan of genotypes with high dispersal capacity, especially in non-reproducing females. Butterflies use body reserves for somatic maintenance and reproduction, but different resources (in thorax versus abdomen) are used under dissimilar conditions, with some interactions with the Pgi genotype. These results indicate life-history trade-offs that involve resource allocation and genotype×environment interactions, and these trade-offs are likely to contribute to the maintenance of Pgi polymorphism in the natural populations.