Cryptochrome, Compound Eyes, Hofbauer-Buchner Eyelets, and Ocelli Play Different Roles in the Entrainment and Masking Pathway of the Locomotor Activity Rhythm in the Fruit Fly Drosophila Melanogaster

All five photoreceptors and photopigments in Drosophila melanogaster significantly contribute to light reception and circadian clock synchronization.

• The compound eyes are crucial for entrainment to extreme photoperiods and for adjusting the phase of activity rhythms.
• Flies can distinguish long days from constant light primarily due to the function of their compound eyes.
• Light exposure promotes activity at lights-on and inhibits it during darkness, highlighting the compound eyes' role in these masking effects.
• Cryptochrome supports lengthening of the activity period under long days but is more essential for synchronization to short days.
• Cryptochrome also influences the aftereffects of photoperiod changes on the internal clock.
• Roles of other photoreceptors remain less clear and are challenging to evaluate.

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