Fig. 1

Schematic drawing of evolved lines. The fluctuation line was exposed to increasingly cooler and more fluctuating, daily temperatures, maintaining the upper thermal limit but reducing the lower thermal limit by 2 °C each generation until the sixth generation experienced a temperature fluctuation between 17 and 27 °C per day (blue). The constant-decline evolved line was reared such that each generation experienced a constant temperature, but this temperature was decreased by 2 °C at the start of each new generation (red). Control conditions were maintained at a constant 27 °C over all generations (grey). Depicted frequency of temperature fluctuations is not to scale