Analysis of the genetically tractable crustacean Parhyale hawaiensis reveals the organisation of a sensory system for low-resolution vision Analysis of the genetically tractable crustacean Parhyale hawaiensis reveals the organisation of a sensory system for low-resolution vision

International audienceBackground: Arthropod eyes have diversified during evolution to serve multiple needs, such as finding mates,hunting prey and navigating in complex surroundings under varying light conditions. This diversity is reflected in theoptical apparatus, photoreceptors and neural circuits that underpin vision. Yet our ability to genetically manipulate thevisual system to investigate its function is largely limited to a single species, the fruit fly Drosophila melanogaster. Here,we describe the visual system of Parhyale hawaiensis, an amphipod crustacean for which we have established tailoredgenetic tools.Results: Adult Parhyale have apposition-type compound eyes made up of ~50 ommatidia. Each ommatidium containsfour photoreceptor cells with large rhabdomeres (R1–4), expected to be sensitive to the polarisation of light, and onephotoreceptor cell with a smaller rhabdomere (R5). The two types of photoreceptors express different opsins, belongingto families with distinct wavelength sensitivities. Using the cis-regulatory regions of opsin genes, we establishedtransgenic reporters expressed in each photoreceptor cell type. Based on these reporters, we show that R1–4 andR5 photoreceptors extend axons to the first optic lobe neuropil, revealing striking differences compared with thephotoreceptor projections found in related crustaceans and insects. Investigating visual function, we show thatParhyale have a positive phototactic response and are capable of adapting their eyes to different levels of lightintensity.Conclusions: We propose that the visual system of Parhyale serves low-resolution visual tasks, such as orientation andnavigation, based on broad gradients of light intensity and polarisation. Optic lobe structure and photoreceptorprojections point to significant divergence from the typical organisation found in other malacostracan crustaceans andinsects, which could be associated with a shift to low-resolution vision. Our study provides the foundation for researchin the visual system of this genetically tractable species