NEARGARDER, G.G.; DAHLHOFF, E.P.; RANK, N.E.: Effect of PGI genotype and temperature exposure on thermal tolerance of the willow leaf beetle Chrysomela aeneicollis

Natural selection may act on loci coding for polymorphic metabolic enzymes when genotypes differ in tolerance to temperature extremes. Allele frequency variation at the glycolytic enzyme locus phosphoglucose isomerase (PGI) relates to habitat temperature in the montane leaf beetle, Chrysomela aeneicollis. This suggests that PGI may be under natural selection. We measured the relationship between PGI genotype and the beetles’ tolerance to extreme temperatures using two methods, the critical thermal maximum (CTMax) and measurement of mortality levels at extreme temperatures (LT50). We determined whether thermal tolerance is affected by an interaction between PGI genotype and previous exposure to non-lethal temperatures. We conducted these experiments with both adults and larvae. We found that thermal tolerance depends on an interaction between PGI genotype and previous exposure to non-lethal temperatures. We also found that thermal tolerance varies among populations and life stages. Adults showed higher thermal tolerance than larvae. Adults that had overwintered were more thermally tolerant than adults that had recently emerged from the pupal stage. The relationship between PGI genotype and thermal tolerance suggests a possible mechanism for natural selection on PGI in this insect.