• thermal selection;
  • temperature adaptation;
  • phosphoglucose isomerase;
  • chill-coma recovery;
  • heat-knock down


  • 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.