How external cues modulate the behavioral output of an animal:Immediate effects of light on rhythmic eclosion behavior in Drosophila

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An appropriate daily timing of behavior is of critical importance for animal fitness. Light shapes the daily timing in two ways: (1) the cyclic change in light intensity acts as an entraining signal, synchronizing the endogenous (circadian) timing system to appropriately adjust an organism to the 24h environmental period; (2) light directly modulates behavior by increasing alertness, locomotion, body temperature and heart rate in diurnal animals including humans and by suppressing activity and promoting sleep in nocturnal animals. These immediate light effects are independent of the circadian clock and since they often obscure (“mask”) circadian behaviors, they are also called “masking” effects of the clock. The immediate light effects are essential for appropriate responses of the animal to changes in the environment and for sharpening the behavioral output. In Drosophila melanogaster, the immediate light effects are mediated by the eyes and most evident as a lights-on response in a well described behavioral rhythm of the fly – the emergence rhythm of the adult insect from the pupa, called eclosion. Eclosion is gated by the circadian clock to the early day to prevent desiccation and enhance survival rate. A light stimulus induces a rapid increase in eclosion rate, the lights-on effect.Here we will use eclosion as a behavioral readout to describe the neuronal circuitry underlying effects of external light stimuli in Drosophila melanogaster. We aim to unravel the neuronal principles of immediate light responses using genetics, behavioral analysis, light microscopy and live cell imaging. The proposed project will - for the first time - untangle the neuronal mechanisms underlying immediate light responses and thereby give novel insights into the fundamental principles of how external cues modulate the brain activity and, thus, the behavioral output of animals.