Research Paper Volume 15, Issue 2 pp 396—420

Figure 7. Uncoupling between light schedules and the circadian clock does not affect Drosophila lifespan. (A) Experimental design and lifespan predictions when Drosophila with free running periods (FRPs) of 18, 24, and 27 hours were exposed to corresponding light cycles. We predicted as day length further deviates from FRP, that lifespan will be negatively impacted (red arrows) and having a FRP that corresponds with the day length be beneficial to lifespan (green arrows). (B) Free running period of 7-day old flies of the genotypes used in the lifespan experiments (grey quadrant), and activity period when exposed to the three light cycles used (green, red and blue quadrants). Clk856-Gal4 x UAS-DBT^S (short day) exhibited a mean period length of 17.8 hours (SD = 0.34) and Clk856-Gal4xUAS-DBT^L (long day) showed a mean period length of 26.8 hours (SD = 0.61). Normal-day CLK856-GAL4 x w¹¹¹⁸ (normal day) had a period length of 23.9 hours (SD = 0.19). When exposed to environmental light all flies had an activity rhythm corresponding with the photoperiod. Light cycle day length during recording period is denoted at the top of each colored box. (C) After three weeks under light cycles all genotypes were placed in free running conditions and all genotypes reverted to their endogenous free running period. When comparing within a genotype there were no effects of rearing photoperiod, Clk856-Gal4 x w¹¹¹⁸ (27 hr n = 15, 24 hr n = 16, 18 hr n = 15; P = 0.934), Clk856-Gal4 x UAS-DBT^L (27 hr n = 10, 24 hr n = 15, 18 hr n = 14; P = 0.689), and Clk856-Gal4 x UAS-DBT^S (27 hr n = 12, 24 hr n = 13, 18 hr n = 12; P = 0.709). Previous light cycle day length is denoted at the top of each colored box. (D–F) Lifespan of Clk856-Gal4 x UAS-DBT^S, Clk856-Gal4 x UAS-DBT^L, and Clk856-Gal4 x w¹¹¹⁸ was not influenced by environmental light cycle, with all genotypes showing no significant effect of light cycle on lifespan (D) short (18 hr n = 157, 24 hr n = 151, 27 hr n = 157; P = 0.615), (E) long (18 hr n = 153, 24 hr n = 149, 27 hr n = 155; P = 0.407), and (F) Gal4 control (18 hr n = 148, 24 hr n = 150, 27 hr n = 143; P = 0.554).