Preliminary evidence for photochemical ageing in Drosophila.
Drosophila melanogaster (Oregon R) males were exposed to visible light intensities varying from 0.3 to 7300 lux at environmental temperatures of 30, 35 and 37 degrees C, on a 12-h light/dark diurnal rhythm. At 30 degrees C reducing the light exposure from 7300 to 4 lux increased the median life span by 141%. At 35 degrees C reducing the light exposure from 4650 to 0.3 lux increased the life span by 389%. At 37 degrees C a reduction from 6580 to 0.3 lux increased life span by 453%. Even dim light (65 lux) affected life span in a negative manner. Two phases of response to light were identified, with a slow change in life span occurring below 400 lux and a more rapid rate of change above 400 lux. We conclude that visible light may be a major factor in the ageing process for Drosophila and that photochemical effects may contribute to senescence in other organisms. Possible alternative reasons for the effect of light on the life span of Drosophila include changes in body temperature, physical activity and oxygen consumption.