per has an epistatic effect on MAN1 in period length determination. A, C Double-plotted representative actograms of the indicated genotypes. Flies were monitored in LD for 4 days and then DD for 7 days. Gray shades indicate dark phases. B The period and power of the DD locomotor rhythm of MAN1RNAi flies over-expressing per. D The period and power of the DD locomotor rhythm of MAN1RNAi flies carrying the perL mutation. Error bars represent SEM. Digits on the bar are the number of flies tested. Percentage of rhythmicity is indicated above the bars (P < 0.001, one-way ANOVA, **/##P < 0.01, ***/###P < 0.001, * vs MAN1-RNAi flies, #vs over-expression or mutant flies, Tukey’s multiple comparison test). G4, GAL4; U, UAS.