Fig. 1.

A phase response curve (PRC) to light inDrosophila Ananassae. (A-C) After lights-off on the last day of a 12:12 LD schedule, independent groups of flies were given a single pulse of white fluorescent light (600 lx, 15 min) at one of the 11 hours associated with the subjective evening, or within half-hour increments near the previous LD schedule’s transitions (CT12.5, 13.5, 22.5, and 23.5). They were then kept in DD. The phase shift observed in each fly’s activity rhythm is shown in scatter plot (1 circle = 1 animal) for both behavioral onsets (A; black circles) and offsets (B; gray circles). The average resetting response (± SEM) for the onset and offset markers are graphed side-by-side for each circadian timepoint tested in panel C. Asterisks indicate onset and offset responses that were statistically different (p < 0.05). Delays are plotted in hours with negative numbers, while advances are plotted with positive numbers. A separate group of flies was treated with flashes of xenon light (4ms, 1 Hz, 205 lx, 15 min) at CT13 (insert, salmon color circles). For comparison’s sake, the broken dotted lines at +3 h and -4 h define the amplitude of phase shifts usually observed after light administration in the delay and advance zones of melanogaster (Hall and Rosbash, 1987, Suri et al., 1998). Data were collected from the following number of flies: 34 (CT12.5), 85 (CT13), 37 (CT13.5), 33 (CT14), 30 (CT15), 25 (CT16), 70 (CT17), 30 (CT18), 30 (CT19), 22 (CT20), 30 (CT21), 33 (CT22), 37 (CT22.5), 92 (CT23), 35 (CT23.5), and 22 (Xenon CT13).