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

Summary1 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.