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
Résumé
Background: 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 the
optical apparatus, photoreceptors and neural circuits that underpin vision. Yet our ability to genetically manipulate the
visual 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 tailored
genetic tools.
Results: Adult Parhyale have apposition-type compound eyes made up of ~50 ommatidia. Each ommatidium contains
four photoreceptor cells with large rhabdomeres (R1–4), expected to be sensitive to the polarisation of light, and one
photoreceptor cell with a smaller rhabdomere (R5). The two types of photoreceptors express different opsins, belonging
to families with distinct wavelength sensitivities. Using the cis-regulatory regions of opsin genes, we established
transgenic reporters expressed in each photoreceptor cell type. Based on these reporters, we show that R1–4 and
R5 photoreceptors extend axons to the first optic lobe neuropil, revealing striking differences compared with the
photoreceptor projections found in related crustaceans and insects. Investigating visual function, we show that
Parhyale have a positive phototactic response and are capable of adapting their eyes to different levels of light
intensity.
Conclusions: We propose that the visual system of Parhyale serves low-resolution visual tasks, such as orientation and
navigation, based on broad gradients of light intensity and polarisation. Optic lobe structure and photoreceptor
projections point to significant divergence from the typical organisation found in other malacostracan crustaceans and
insects, which could be associated with a shift to low-resolution vision. Our study provides the foundation for research
in the visual system of this genetically tractable species.
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