Fig. 3

Schematic overview of resistance mutations with temperature-specific effects. An increased activity of AChE at higher temperature results in a major challenge for neuronal signaling homeostasis because acetylcholine is degraded at higher levels (top panel). Because insecticide resistance mutations destabilize AChE, less acetylcholine is degraded in individuals carrying the resistance mutations (1a), independent of the temperature. In the hot, this provides them with a fitness advantage compared to individuals without the destabilizing resistance mutations (1b) since those suffer from the excess activity of the fully functional enzyme at high temperature. The inverse applies to the cold environment in which the fully functional 1b haplotype class can better compensate for the reduced enzymatic activity. Because the two alleles result in AChE activity which is closer to the optimum at different temperatures, the fitness of the two alleles differs at hot and cold temperatures (bottom panel)