Navigational strategies underlying temporal phototaxis inDrosophilalarvae

Navigating across light gradients is essential for survival for many animals. However, we still have a poor understanding of the algorithms that underlie such behaviors. Here we develop a novel phototaxis assay for Drosophila larvae in which light intensity is always spatially uniform but updates depending on the location of the animal in the arena. Even though larvae can only rely on temporal cues in this closed-loop setup, we find that they are capable of finding preferred areas of low light intensity. Further detailed analysis of their behavior reveals that larvae turn more frequently and that heading angle changes increase when they experience brightness increments over extended periods of time. We suggest that temporal integration of brightness change during runs is an important – and so far largely unexplored – element of phototaxis. Summary statement Using a novel closed-loop behavioral assay, we show that Drosophila larvae can navigate light gradients exclusively using temporal cues. Analyzing and modeling their behavior in detail, we propose that larvae achieve this by integrating brightness change during runs.