Abstract
BackgroundArthropod 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.ResultsAdult 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.ConclusionsWe 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.
Highlights
Arthropods have elaborate visual systems that are capable of serving a wide range of tasks, including orientation and navigation, prey capture, habitat selection and communication, in diverse environments
The structure of Parhyale eyes suggests that their visual system serves low-resolution visual tasks
Optic lobe and photoreceptor projections diverge from the typical organisation found in malacostracan crustaceans and insects, possibly reflecting this shift to low-resolution vision
Summary
Arthropods have elaborate visual systems that are capable of serving a wide range of tasks, including orientation and navigation, prey capture, habitat selection and communication, in diverse environments (see [1]). Depending on the life habits of individual species, the needs for spatial resolution, motion detection, sensitivity to colour or Compound eyes, the most common and best-studied type of arthropod eye, are made up of multiple repeated units. Differences in the types, morphology and arrangement of photoreceptors influence the capacity to detect colour and polarised light [1, 5]. 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. We describe the visual system of Parhyale hawaiensis, an amphipod crustacean for which we have established tailored genetic tools
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