Schematic diagram of the experiment
Fruit flies were collected from two sites in Australia: a northern site that had a warm sub-tropical climate, and a southern site that had a cold temperate climate. The flies from the two sites were then interbred in the laboratory. The initial stage, called admixture, took place at 25ºC, and the later generations were reared in bottles maintained at different temperatures ranging from warm to cold. While two bottles were maintained in constant 19ºC and 25ºC, the temperature in the other two bottles simulated the thermal conditions of the two sites from where the flies were collected (fluctuating cold and warm).