Phosphoglucose isomerase genotype affects life‐history traits and cold stress resistance in a Copper butterfly

Abstract

1 Accumulating evidence suggests that the phosphoglucose isomerase (PGI) locus is under thermal selection. In the Copper butterfly Lycaena tityrus PGI allele frequencies show altitudinal variation, with a single genotype occurring in c. 90% of high-altitude animals. In low-altitude populations variation at this locus is much higher. 2 Here, we investigate variation in life-history traits and temperature stress resistance across PGI genotypes in L. tityrus from different lowland populations reared at two temperatures (19 and 24 °C). 3 PGI genotype significantly affected larval and pupal development time, growth rate, pupal mass and chill-coma recovery time, but had no effect on heat knock-down resistance. The latter suggests that heat and cold stress resistance are based on differential mechanisms. 4 As expected temperature also influenced all traits under investigation, its effect being more pronounced compared to that of PGI genotype (except for pupal mass). 5 Patterns found for the PGI genotype dominating in high-altitude populations were consistent with those found for high-altitude animals. Therefore, and because of the direct link between PGI genotype and cold stress resistance, we conclude that PGI is likely to contribute to thermal adaptation in L. tityrus. 6 Genotypes promoting rapid development and largest body size were rather rare, suggesting weak selection on both traits and/or rather high associated costs.