title: Normal vision can compensate for the loss of the circadian clock.
abstract: Circadian clocks are thought to be essential for timing the daily activity of animals, and consequently increase fitness. This view was recently challenged for clock-less fruit flies and mice that exhibited astonishingly normal activity rhythms under outdoor conditions. Compensatory mechanisms appear to enable even clock mutants to live a normal life in nature. Here, we show that gradual daily increases/decreases of light in the laboratory suffice to provoke normally timed sharp morning (M) and evening (E) activity peaks in clock-less flies. We also show that the compound eyes, but not Cryptochrome (CRY), mediate the precise timing of M and E peaks under natural-like conditions, as CRY-less flies do and eyeless flies do not show these sharp peaks independently of a functional clock. Nevertheless, the circadian clock appears critical for anticipating dusk, as well as for inhibiting sharp activity peaks during midnight. Clock-less flies only increase E activity after dusk and not before the beginning of dusk, and respond strongly to twilight exposure in the middle of the night. Furthermore, the circadian clock responds to natural-like light cycles, by slightly broadening Timeless (TIM) abundance in the clock neurons, and this effect is mediated by CRY.
authors.affiliation: Neurobiology and Genetics, Theodor Boveri Institute, Biocenter, University of Würzburg, Würzburg, Germany.
authors.forename: Matthias
authors.initials: M
authors.lastname: Schlichting
authors.affiliation: Neurobiology and Genetics, Theodor Boveri Institute, Biocenter, University of Würzburg, Würzburg, Germany.
authors.forename: Pamela
authors.initials: P
authors.lastname: Menegazzi
authors.affiliation: Neurobiology and Genetics, Theodor Boveri Institute, Biocenter, University of Würzburg, Würzburg, Germany charlotte.foerster@biozentrum.uni-wuerzburg.de.
authors.forename: Charlotte
authors.initials: C
authors.lastname: Helfrich-Förster
mesh_terms: D000818:Animals; D057906:Circadian Clocks; D054910:Compound Eye, Arthropod / Q000502:physiology; D056931:Cryptochromes / Q000235:genetics* / Q000502:physiology; D004331:Drosophila melanogaster / Q000235:genetics / Q000502:physiology*; D008027:Light; D008124:Locomotion; D008297:Male; D017440:Photoperiod
chemical_list: D056931:Cryptochromes
keywords: circadian rhythms; period; timeless