How a Light-Sensing Protein and the Visual System Work Oppositely to Adjust Evening Activity in Fruit Flies During Long Days

The evening peak of activity in fruit flies may be limited in its ability to track dusk during long days due to the influence of cryptochrome.

• Two distinct circadian oscillators regulate the morning and evening activity peaks in fruit flies.
• The evening peak can adjust its timing based on the changes in day length.
• Cryptochrome in specific neurons reduces the evening peak's ability to align with dusk during longer photoperiods.
• Light signals from the fly's visual system enhance the evening peak's tracking of dusk.
• Cryptochrome signaling dampens the activity of a key protein involved in the circadian rhythm during long days.

Simplified