Synergic Entrainment of Drosophila’s Circadian Clock by Light and Temperature

Abstract

Daily light and temperature cycles are considered the most important zeitgebers for circadian clocks in many organisms. The influence of each single zeitgeber on the clock has been well studied, but little is known about any synergistic effects of both zeitgebers on the clock. In nature, light and temperature show characteristic daily oscillations with the temperature rising during the light phase and reaching its maximum in the late afternoon. Here, we studied behavioral and molecular rhythms in Drosophila melanogaster under simulated natural low light-dark (LD) and temperature (T) cycles that typically occur during the September equinox. Wild-type flies were either subjected to simulated LD or T cycles alone or to a combination of both. Behavioral rhythms and molecular rhythms in the different clock neurons were assessed under the 3 different conditions. Although behavioral rhythms entrained to all conditions, the rhythms were most robust under the combination of LD and T cycles. The clock neurons responded differently to LD and T cycles. Some were not entrained by T cycles alone; others were only slightly entrained by LD cycles alone. The amplitude of the molecular cycling was not different between LD alone and T cycles alone; but LD alone could set the pacemaker neurons to similar phases, whereas T cycles alone could not. The combination of the 2 zeitgebers entrained all clock neurons not only with similar phase but also enhanced the amplitude of Timeless cycling in the majority of cells. Our results show that the 2 zeitgebers synergistically entrain behavioral and molecular rhythms of Drosophila melanogaster.

Circadian rhythms identified in Caenorhabditis elegans by in vivo long-term monitoring of a bioluminescent reporter

“…Interestingly, D. melanogaster exhibits a strong preference for a temperature rhythm in which the temperature is lower in the morning and higher at dusk: The preferred temperature increases gradually from morning (ZT1-3) to peak in the evening (ZT10-12) (53). A similar synergistic effect was described in flies, in which a combination of light and temperature zeitgebers reinforced entrainment at the molecular and behavioral level (54). In our current study, the phase relationship to the LD/ CW cycle showed a marked dependency on temperature, reflecting some adaptive aspects of the rhythm related to the natural environment of the nematode.…”

Phototransduction and clock gene expression in the troglobiont beetlePtomaphagus hirtusof Mammoth cave

“…Consistent with this last scenario, an impact of environmental temperature oscillations on circadian rhythm regulation has been documented in a number of insects including cave-adapted carabid and catopsid beetles (for reviews, see Lamprecht and Weber, 1992;Page, 1985;Rence and Loher, 1975;Tomioka and Chiba, 1989;Weber et al, 1995;Yoshii et al, 2009 Mammoth cave system but entrance areas, exposed to air currents, show variation in humidity and temperature (Barr and Kuehne, 1971). Moreover, there is evidence that the distribution of bottomdwelling cave arthropods including P. hirtus is temperature and humidity dependent (Barr and Kuehne, 1971).…”

“…While it is tempting to speculate that P. hirtus measures diurnal light level changes in the disphotic cave environment, the clock gene network may be environmentally adjusted by other stimuli such as temperature (Collins et al, 2004;Yoshii et al, 2009). Consistent with this last scenario, an impact of environmental temperature oscillations on circadian rhythm regulation has been documented in a number of insects including cave-adapted carabid and catopsid beetles (for reviews, see Lamprecht and Weber, 1992;Page, 1985;Rence and Loher, 1975;Tomioka and Chiba, 1989;Weber et al, 1995;Yoshii et al, 2009 Mammoth cave system but entrance areas, exposed to air currents, show variation in humidity and temperature (Barr and Kuehne, 1971).…”

Temporal calcium profiling of specific circadian neurons in freely moving flies

“…The daily oscillations of clock proteins, such as period (PER) and timeless (TIM), are quite well synchronized in all circadian neuron groups (16,17). However, their diverse functions suggest that their peak neuronal activities, when they achieve maximal firing rates, occur at different circadian times.…”