Fig. 4

Reduced and more fragmented sleep in high altitude flies continues even in constant light conditions where circadian clock function is abolished. a-f Shown are group averages of fly activity (a and c), sleep levels (b and d), median sleep bout length (e), and number of sleep bouts (f) for Cameroon male flies from either the high (blue line) or low (red line) altitude groups. For this experiment, two representative lines were used for each altitude; Cameroon low altitude (CO1, CO4); Cameroon high altitude (CM16, CM54). Flies were maintained at 25 °C and entrained for five days in LD. Subsequently, half of the high and low altitude groups were placed in constant darkness (DD), whereas the other half was placed in constant light (LL). White, black, dark gray, and light gray horizontal bars below panels represent 12-h periods of light, dark, ‘subjective daytime’ in DD, and ‘subjective nighttime’ in LL, respectively. In LL, comparison of low and high altitude flies for daily activity profiles (c), daily sleep levels (d), median sleep bout length (e), and number of sleep bouts (f) showed highly significant differences (one-way ANOVA, p < 0.0001). Similar results showing that high altitude flies exhibit less total sleep that is more fragmented in LL compared to low altitude flies were also obtained with flies from Kenya (data not shown)