Reduced sleep in temperate flies continues in constant light conditions where circadian clock function is abolished.

(A, B) Shown are group averages of sleep levels in min during 30-min bins. Young adult male flies were maintained at 25°C and entrained for five days in LD. Subsequently, half of the tropical and temperate groups were placed in constant light (LL; panel A), whereas the other half was placed in constant darkness (DD; panel B). Time 0 (hr) begins with the fifth day of LD followed by the subsequent days in LL or DD. For the data shown in this figure, 16 individual flies from each of the 8 lines representing each region (tropical and temperate) were analyzed and data pooled. Fly lines used are as follows; tropical, HB22, HB25, HB27, HB106, HB108, GT46, GT92, GT110; temperate, S3, S4, S7, S8, S12, S22, S28, S34. White, black, stripped, and light gray horizontal bars below panels represent 12-hr periods of light, dark, ‘subjective nighttime in LL, and ‘subjective daytime’ in DD, respectively. In LL and DD, comparison of tropical and temperate flies for daily sleep levels showed highly significant differences (one-way ANOVA for first 3 days in LL or DD; panel A, p<0.0001; panel B, 0.0091).