Abstract
Under standard laboratory conditions of rectangular light/dark cycles and constant warm temperature, Drosophila melanogaster show bursts of morning (M) and evening (E) locomotor activity and a "siesta" in the middle of the day. These M and E components have been critical for developing the neuronal dual oscillator model in which clock gene expression in key cells generates the circadian phenotype. However, under natural European summer conditions of cycling temperature and light intensity, an additional prominent afternoon (A) component that replaces the siesta is observed. This component has been described as an "artifact" of the TriKinetics locomotor monitoring system that is used by many circadian laboratories world wide. Using video recordings, we show that the A component is not an artifact, neither in the glass tubes used in TriKinetics monitors nor in open-field arenas. By studying various mutants in the visual and peripheral and internal thermo-sensitive pathways, we reveal that the M component is predominantly dependent on visual input, whereas the A component requires the internal thermo-sensitive channel transient receptor potential A1 (TrpA1). Knockdown of TrpA1 in different neuronal groups reveals that the reported expression of TrpA1 in clock neurons is unlikely to be involved in generating the summer locomotor profile, suggesting that other TrpA1 neurons are responsible for the A component. Studies of circadian rhythms under seminatural conditions therefore provide additional insights into the molecular basis of circadian entrainment that would otherwise be lost under the usual standard laboratory protocols.
Highlights
Under standard laboratory conditions of rectangular light/dark cycles and constant warm temperature, Drosophila melanogaster show bursts of morning (M) and evening (E) locomotor activity and a “siesta” in the middle of the day
By using video recordings of fly circadian activity in glass tubes and open-field arenas, we investigate whether the A component is an artifact
Among several unexpected results of the seminatural studies of locomotor activity of Vanin et al, the most attention has been generated by the finding that flies are highly active under warm natural conditions during the afternoon, giving rise to the A component (3)
Summary
Under standard laboratory conditions of rectangular light/dark cycles and constant warm temperature, Drosophila melanogaster show bursts of morning (M) and evening (E) locomotor activity and a “siesta” in the middle of the day These M and E components have been critical for developing the neuronal dual oscillator model in which clock gene expression in key cells generates the circadian phenotype. In Drosophila melanogaster, locomotor rhythms studied in seminatural conditions reveal that deeply held, laboratory-derived assumptions may require significant revision These include the crepuscular nature of fly activity, the role of the clock in “morning anticipation” and midday “siesta,” the requirement for clock gene expression in the central clock neurons for entrainment, and the role of light/dark (LD) cycles as the most important environmental Zeitgeber (“time giver”) in entraining the clock (3). Vanin et al (3) observed that in the wild the phase of various features of circadian locomotor behavior such as the morning (M) and evening (E) components was best predicted by
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