Cold rearing improves cold-flight performance in Drosophila via changes in wing morphology

We use a factorial experimental design to test whether rearing at colder temperatures shifts the lower thermal envelope for flight of Drosophila melanogaster Meigen to colder temperatures. D. melanogaster that developed in colder temperatures (15 degrees C) had a significant flight advantage in cold air compared to flies that developed in warmer temperatures (28 degrees C). At 14 degrees C, cold-reared flies failed to perform a take-off flight similar to 47% of the time whereas warm-reared flies failed similar to 94% of the time. At 18 degrees C, cold- and warm-reared flies performed equally well. We also compared several traits in cold- and warm-developing flies to determine if cold-developing flies had better flight performance at cold temperatures due to changes in body mass, wing length, wing loading, relative flight muscle mass or wing-beat frequency. The improved ability to fly at low temperatures was associated with a dramatic increase in wing area and an increase in wing length (after controlling for wing area). Flies that developed at 15 degrees C had similar to 25% more wing area than similarly sized flies that developed at 28 degrees C. Cold-reared flies had slower wing-beat frequencies than similarly sized flies from warmer developmental environments, whereas other traits did not vary with developmental temperature. These results demonstrate that developmental plasticity in wing dimensions contributes to the improved flight performance of D. melanogaster at cold temperatures, and ultimately, may help D. melanogaster live in a wide range of thermal environments.