Fig. 1. Interspecific circadian differences in D. sechellia and D. melanogaster.
a, D. melanogaster (Dmel) subgroup phylogeny (left) and ranges (right) of Dmel (blue) and D. sechellia (Dsec) (orange), with approximate collection sites of strains. b, Approximate photoperiod variation (www.srrb.noaa.gov) at collection sites of Dmel (left) and Dsec (right) strains. c, Top, mean normalized activity of Dmel and Dsec under the indicated photoperiods. Yellow and grey bars indicate lights-on and lights-off, respectively; vertical dashed lines indicate average timing of the evening peak; error bars represent s.e.m. Middle, box plots (Methods) depicting evening peak time for individual flies under each photoperiod. Bottom, pie charts representing the proportion of flies that maintained rhythmic behaviour (colour) or no significant periodicity (grey). n, 12:12 h LD: CS (18), OR (21), 07 (24), 28 (19); 14:10 h LD: CS (22), OR (22), 07 (19), 28 (13); 16:8 h LD: CS (18), OR (21), 07 (24), 28 (19); 18:6 h LD: CS (22), OR (23), 07 (21), 28 (11); 20:4 h LD: CS (21), OR (22), 07 (19), 28 (18). d, Left, mean normalized activity of Dmel and Dsec under 12:12 h LD during the morning activity peak (−6 to +6 h data from c). Dashed boxes highlight the predawn period. Right, mean normalized activity of individual flies within the predawn period. n: CS (89), OR (93), 07 (95), 28 (91). e, Double-plotted actograms depicting the transition from the last 2 days of 12:12 h LD to DD for each strain. Dashed boxes highlight morning activity peak period during DD, −3 to +3 h. n: CS (29), OR (32), 07 (29), 28 (22). Grey bars indicate timing of subjective lights-on during DD. f, Morning peak time, from lights-on, for flies from d. c,d,f, Letters A–D indicate significant differences, P < 0.05 (pairwise Wilcoxon test with Bonferroni correction). E, equinox; S, solstice.