Very dim night light changes daily movement patterns in adult fruit flies

Activity onset in experimental flies occurred approximately 5.4 hours prior to lights-on.

• Experimental flies showed a significant shift in activity onset compared to control flies, which aligned closely with lights-on.
• Despite differing activity onset times, both groups exhibited the same activity offset at lights-off.
• The duration of the active phase and activity passes per fly per cycle were significantly higher in experimental flies than in controls.
• When placed in constant darkness, experimental flies demonstrated a shortened free-running rhythm period, lengthened active phase, and increased activity passes compared to controls.
• The physiological adaptations observed in these flies suggest low sensitivity to dim light is suited for their natural environment.

Simplified