The daily rhythm of adult emergence of holometabolous insects is one of the first circadian rhythms to be studied. In these insects, the circadian clock imposes a daily pattern of emergence by allowing or stimulating eclosion during certain windows of time and inhibiting emergence during others, a process that has been described as “gating.” Although the circadian rhythm of insect emergence provided many of the key concepts of chronobiology, little progress has been made in understanding the bases of the gating process itself, although the term “gating” suggests that it is separate from the developmental process of metamorphosis. Here, we follow the progression through the final stages of Drosophila adult development with single-animal resolution and show that the circadian clock imposes a daily rhythmicity to the pattern of emergence by controlling when the insect initiates the final steps of metamorphosis itself. Circadian rhythmicity of emergence depends on the coupling between the central clock located in the brain and a peripheral clock located in the prothoracic gland (PG), an endocrine gland whose only known function is the production of the molting hormone, ecdysone. Here, we show that the clock exerts its action by regulating not the levels of ecdysone but that of its actions mediated by the ecdysone receptor. Our findings may also provide insights for understanding the mechanisms by which the daily rhythms of glucocorticoids are produced in mammals, which result from the coupling between the central clock in the suprachiasmatic nucleus and a peripheral clock located in the suprarenal gland.

In many animals the circadian rhythm of locomotor activity is controlled by an endogenous circadian clock. Using custom made housing and video tracking software in order to obtain high spatial and temporal resolution, we studied the statistical properties of the locomotor activity of wild type and two clock mutants of Drosophila melanogaster. We show here that the distributions of activity and quiescence bouts for the clock mutants in light-dark conditions (LD) are very different from the distributions obtained when there are no external cues from the environment (DD). In the wild type these distributions are very similar, showing that the clock controls this aspect of behavior in both regimes (LD and DD). Furthermore, the distributions are very similar to those reported for Wistar rats. For the timing of events we also observe important differences, quantified by how the event rate distributions scale for increasing time windows. We find that for the wild type these distributions can be rescaled by the same function in DD as in LD. Interestingly, the same function has been shown to rescale the rate distributions in Wistar rats. On the other hand, for the clock mutants it is not possible to rescale the rate distributions, which might indicate that the extent of circadian control depends on the statistical properties of activity and quiescence.

In many species daily rhythms are endogenously generated by groups of coupled neurons that play the role of a circadian pacemaker. The adaptation of the circadian clock to environmental and seasonal changes has been proposed to be regulated by a dual oscillator system. In order to gain insight into this model, we analyzed the synchronization properties of two fully coupled groups of Kuramoto oscillators. Each group has an internal coupling parameter and the interaction between the two groups can be controlled by two parameters allowing for symmetric or non-symmetric coupling. We show that even for such a simple model counterintuitive behaviours take place, such as a global decrease in synchrony when the coupling between the groups is increased. Through a detailed analysis of the local synchronization processes we explain this behaviour.

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We study the dynamical response under local noise of an excitable ring of FitzHugh-Nagumo units coupled through nearest-neighbor phase-repulsive electric synapses. The system is externally, adiabatically driven by a weak subthreshold periodic signal and independent Gaussian white noises. By varying the coupling strength and the noise intensity, two routes to noise-sustained synchronization are numerically observed and elucidated in terms of the system's non-equilibrium potential. In particular, the threshold noise intensity for synchronization is theoretically predicted and numerically confirmed.