Daytime colour preference in Drosophila depends on the circadian clock and TRP channels.

Light discrimination according to colour can confer survival advantages by guiding animals towards food and shelter and away from potentially harmful situations^1,2. Such colour-dependent behaviour can be learned or innate. Data on innate colour preference in mammals remain controversial³ and there are limited data for simpler organisms^4-7. Here we show that, when given a choice among blue, green and dim light, fruit flies exhibit an unexpectedly complex pattern of colour preference that changes according to the time of day. Flies show a strong preference for green in the early morning and late afternoon, a reduced green preference at midday and a robust avoidance of blue throughout the day. Genetic manipulations reveal that the peaks in green preference require rhodopsin-based visual photoreceptors and are controlled by the circadian clock. The midday reduction in green preference in favour of dim light depends on the transient receptor potential (TRP) channels dTRPA1 and Pyrexia, and is also timed by the clock. By contrast, avoidance of blue light is primarily mediated by multidendritic neurons, requires rhodopsin 7 and the TRP channel Painless, and is independent of the clock. Our findings show that several TRP channels are involved in colour-driven behaviour in Drosophila, and reveal distinct pathways of innate colour preference that coordinate the behavioural dynamics of flies in ambient light.

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