Fig. 1

High altitude flies exhibit more of a ‘cold’ phenotype in daily wake-sleep profiles compared to low altitude flies. a-l Adult male flies from low and high altitudes representing several different locations in Cameroon (a-f) and Kenya (g-l) were kept at the indicated temperature (right of panels) and entrained to five days of 12 h light/12 h dark cycles (LD) followed by constant dark conditions (DD). For each country and temperature, the locomotor activity data of individual flies (16 flies per line) from the same altitude group (low or high) were pooled, and shown are group averages of daily activity rhythms (blue, high altitude group; red, low altitude group). To facilitate comparisons, the peak value in daily activity for each fly was set to 1.0 and the normalized profiles superimposed. For LD, the last three days’ worth of data was pooled; for DD, the first day is shown (DD1). The following fly lines were used in this experiment (see Additional file 1: Table S1 for further details); Cameroon low altitude (CM16, CM17, CM22, CM54, CY1); Cameroon high altitude (CO1, CO2, CO4, CO8, CO10, CO13, CO15, CO16); Kenya low altitude (KM10, KM16, and KM20); Kenya high altitude (KN5, KN6M, KN11M, KN13M, KN19M, KN23M, KO2, KO6, KO10M). Horizontal bars at bottom of panels denote 12-h periods of light (white bar), dark (black bar) and ‘subjective daytime’ in DD (gray bar). ZT, zeitgeber time (hr); CT, circadian time (hr). The results shown in this figure are representative of at least two independent experiments, using the same or additional lines from Cameroon or Kenya (see Additional file 1: Table S1). The results show that during LD high altitude flies from both Cameroon and Kenya exhibit a more pronounced ‘cold-type’ daily activity pattern, highlighted by a shorter and less robust midday siesta, earlier onset of evening activity and later offset of morning activity