Monarch butterfly Cryptochrome 1 loss-of-function mutants reveal differences in light entrainment of 24-hour behavioral rhythms in insects
Light is one of the strongest cues for entrainment of circadian clocks in most organisms. Previous work in Drosophila melanogaster (dm) has shown that entrainment relies on both the visual system and the circadian, blue-light photoreceptor Cryptochrome (dmCRY). Here, we used the monarch butterfly Danaus plexippus (dp) to test conservation of this mechanism among insects and the relative importance of monarch Cryptochrome 1 (dpCry1) in the entrainment of its clock in vivo. We showed that loss of functional dpCry1 abolishes adult circadian eclosion behavior and molecular circadian rhythms in the monarch brain. These rhythms can be restored by entrainment to temperature cycles, demonstrating that the core circadian clock is intact in dpCry1 mutants. Importantly, we showed that rhythmic flight activity is also disrupted in dpCry1 mutants but not in the visually impaired dpNinaB1 mutants, suggesting that unlike Drosophila light-entrainment of the monarch circadian clock relies solely on dpCRY1 photoreception.