Figure 1—

A system to measure MR in single flies. (A) MR was measured through indirect calorimetry. A stop-flow respirometry system measured the CO₂ produced by single flies placed inside of a 70 mm long × 20 mm diameter glass tube. Each fly had access to 1% agar and 5% sucrose. Activity and sleep were measured simultaneously as MR using a Drosophila Locomotor Activity Monitor with three infrared beams running through each behavior chamber. The computer counted the number of beam breaks. (B) A representative 5-minute reading, with the activity in number of beam crosses and the amount of CO₂ produced by each fly over time. (C) The MR and activity for one female fly. (D) The MR and activity for one male fly. (E) The activity of female (N = 24; p < .0001) and male (N = 35; p < .0001) flies in beam crosses per hour, over 12 hours of day and night (two-way ANOVA F_(1,114) = 171.9, p < .0001). Condition-by-sex interaction is significant (two-way ANOVA F_(1,114) = 15.30, p < .001). (F) The MR of female (N = 24; p < .01) and male (N = 35; p < .01) flies as CO₂ produced per hour, over 12 hours of day and night (two-way ANOVA F_(1,114) = 21.27, p < .0001). Condition-by-sex interaction is not significant (two-way ANOVA F_(1,114) = 0.4137, p > .50). (G) Linear regression of absolute vCO₂ readout versus activity of female flies (N = 24 each bin; R² = 0.120) and (H) male flies (N = 35 each bin; R² = 0.064). Gray dashed lines indicate 95% confidence interval. One-way ANOVA comparing the vCO₂ at the 1–10 beam crossings bin to each subsequent beam crossing bin: females >60 crossings (N = 24 each bin; p < .05) and males >60 crossings (N = 35 each bin; p < .05). ANOVA = analysis of variance; IR = infrared.