Loss of functional cryptochrome 1 reduces robustness of 24-hour behavioral rhythms in monarch butterflies

Abstract

Light is one of the strongest cues for entrainment of circadian clocks. While some insect species rely only on visual input, others like <i>Drosophila melanogaster</i> use both the visual system and the deep-brain blue-light photoreceptor cryptochrome for entraining circadian rhythms. Here, we used the monarch butterfly <i>Danaus plexippus</i> (<i>dp</i>), which possesses a light-sensitive <i>cryptochrome 1</i> (<i>dpCry1</i>), to test the conservation of mechanisms of clock entrainment. We showed that loss of functional <i>dpCry1</i> reduced the amplitude and altered the phase of adult eclosion rhythms, and disrupted brain molecular circadian rhythms. Robust rhythms could be restored by entrainment to temperature cycles, indicating a likely functional core circadian clock in <i>dpCry1</i> mutants. We also showed that rhythmic flight activity was less robust in <i>dpCry1</i> mutants, and that visual impairment in <i>dpNinaB1</i> mutants impacted flight suppression at night. Our data suggest that dpCRY1 is a major photoreceptor for light-entrainment of the monarch circadian clock.