View Program - 63rd Annual Drosophila Research Conference

Color and motion are used by many species to identify salient moving objects. They are processed largely independently, but color contributes to motion processing in humans, for example, enabling moving colored objects to be detected when their luminance matches the background. In Drosophila, motion vision was thought to be independent of color vision, based on experiments with blue and green gratings; color inputs to the luminance system had been identified through neurogenetics and connectomics, but these were thought to expand the wavelength sensitivity of the luminance channel. Here, we demonstrate an unexpected, additional contribution of color to motion vision in Drosophila, using a novel display system to present ultraviolet (UV) and green visual patterns to tethered flying flies. We show that Drosophila respond to looming UV discs at all intensities, indicating that color contributes to their motion vision. We further show that behavioral ON-motion responses are more sensitive to UV than for OFF-motion, and this difference is present in all six Drosophila species we tested. Using genetic rescue and silencing, we show that ON-motion UV-sensitivity depends on the UV-sensitive R7 photoreceptors, and using calcium imaging of neural activity we show that ON-motion encoding T4 cells are more sensitive to UV than OFF-motion encoding T5 cells. Calcium imaging of the cells connecting the photoreceptors to T4 reveals a diversity of UV-sensitivity, in which the UV-sensitivity of medulla T4 input cells correlates with that of their most numerous lamina monopolar cell inputs, notably Mi9 and L3. In a parallel connectomics study, we discovered that the majority of R7 inputs to L3 are found in the optic chiasm between the medulla and lamina, and so had been missed in previous work. We hypothesized that if the ability of flies to respond to all intensities of looming UV discs was explained by ON-motion sensitivity to UV, then flies should be motion blind to looming green discs with a UV background, even when they have the same chromatic contrast as UV discs that drive behavioral responses. Remarkably, behavioral experiments confirmed this hypothesis. Together, these results demonstrate that color contributes to motion vision in Drosophila in a way that favors the detection of approaching UV objects. We propose that UV objects are of particular interest to flies, and illustrate how this mechanism generalizes for the detection of approaching colored objects in other visual systems.

Color augments motion vision for detecting approaching objects in Drosophila