Ancestral photoreceptor diversity as the basis of visual behaviour

Animal colour vision is based on comparing signals from different photoreceptors. It is generally assumed that processing different spectral types of photoreceptor mainly serves colour vision. Here I propose instead that photoreceptors are parallel feature channels that differentially support visual-motor programmes like motion vision behaviours, prey capture and predator evasion. Colour vision may have emerged as a secondary benefit of these circuits, which originally helped aquatic vertebrates to visually navigate and segment their underwater world. Specifically, I suggest that ancestral vertebrate vision was built around three main systems, including a high-resolution general purpose greyscale system based on ancestral red cones and rods to mediate visual body stabilization and navigation, a high-sensitivity specialized foreground system based on ancestral ultraviolet cones to mediate threat detection and prey capture, and a net-suppressive system based on ancestral green and blue cones for regulating red/rod and ultraviolet circuits. This ancestral strategy probably still underpins vision today, and different vertebrate lineages have since adapted their original photoreceptor circuits to suit their diverse visual ecologies.

Miniature bioinspired artificial compound eyes: microfabrication technologies, photodetection and applications

As an outstanding visual system for insects and crustaceans to cope with the challenges of survival, compound eye has many unique advantages, such as wide field of view, rapid response, infinite depth of field, low aberration and fast motion capture. However, the complex composition of their optical systems also presents significant challenges for manufacturing. With the continuous development of advanced materials, complex 3D manufacturing technologies and flexible electronic detectors, various ingenious and sophisticated compound eye imaging systems have been developed. This paper provides a comprehensive review on the microfabrication technologies, photoelectric detection and functional applications of miniature artificial compound eyes. Firstly, a brief introduction to the types and structural composition of compound eyes in the natural world is provided. Secondly, the 3D forming manufacturing techniques for miniature compound eyes are discussed. Subsequently, some photodetection technologies for miniature curved compound eye imaging are introduced. Lastly, with reference to the existing prototypes of functional applications for miniature compound eyes, the future development of compound eyes is prospected.

Functional Anatomy of Split Compound Eyes of the Whirligig Beetles Dineutus mellyi (Coleoptera: Gyrinidae)

The functional anatomy of the split compound eyes of whirligig beetles Dineutus mellyi (Coleoptera: Gyrinidae) was examined by advanced microscopy and microcomputed tomography. We report the first 3D visualization and analysis of the split compound eyes. On average, the dorsal and ventral eyes contain 1913 ± 44.5 facets and 3099 ± 86.2 facets, respectively. The larger area of ventral eyes ensures a higher field of vision underwater. The ommatidium of the split compound eyes is made up of laminated cornea lenses that offer protection against mechanical injuries, bullet-shaped crystalline cones that guide light to the photoreceptive regions, and screening pigments that ensure directional light passage. The photoreceptive elements, made up of eight retinular cells, exhibit a tri-tiered rhabdom structure, including the upper distal rhabdom, a clear zone that ensures maximum light passage, and an enlarged lower distal rhabdom that ensures optimal photon capture.

Comparative study of spectral sensitivity, irradiance sensitivity, spatial resolution and temporal resolution in the visual systems of Ocypode quadrata and Aratus pisonii

Early pioneering studies by Autrum on terrestrial arthropods first revealed that the visual systems of arthropods reflected their lifestyles and habitats. Subsequent studies have examined and confirmed Autrum's hypothesis that visual adaptions are driven by predator-prey interactions and activity cycles, with rapidly moving predatory diurnal species generally possessing better temporal resolution than slower moving nocturnal species. However, few studies have compared the vision between diurnal herbivores and nocturnal predators. In this study, the visual physiology of a nocturnal fast-moving predatory crab, the Atlantic ghost crab (Ocypode quadrata) and a diurnal herbivorous crab, the mangrove tree crab (Aratus pisonii), was examined. Spectral sensitivity, irradiance sensitivity and temporal resolution of the crabs were quantified using the electroretinogram (ERG), while the spatial resolution was calculated utilizing morphological methods. Both O. quadrata and A. pisonii had a single dark-adapted spectral sensitivity peak (494 and 499 nm, respectively) and chromatic adaptation had no effect on their spectral sensitivity, indicating that both species have monochromatic visual systems. The temporal resolution of O. quadrata was not significantly different from that of A. pisonii, but O. quadrata did possess a significantly greater spatial resolution and irradiance sensitivity. Both species possess an acute zone in the anterior region of their eyes. The data presented in this study will aid in the current understanding of the correlation between visual physiology and the life history of the animal.

Nanomaterial-Based Artificial Vision Systems: From Bioinspired Electronic Eyes to In-Sensor Processing Devices

High-performance robotic vision empowers mobile and humanoid robots to detect and identify their surrounding objects efficiently, which enables them to cooperate with humans and assist human activities. For error-free execution of these robots' tasks, efficient imaging and data processing capabilities are essential, even under diverse and complex environments. However, conventional technologies fall short of meeting the high-standard requirements of robotic vision under such circumstances. Here, we discuss recent progress in artificial vision systems with high-performance imaging and data processing capabilities enabled by distinctive electrical, optical, and mechanical characteristics of nanomaterials surpassing the limitations of traditional silicon technologies. In particular, we focus on nanomaterial-based electronic eyes and in-sensor processing devices inspired by biological eyes and animal visual recognition systems, respectively. We provide perspectives on key nanomaterials, device components, and their functionalities, as well as explain the remaining challenges and future prospects of the artificial vision systems.

Views from 'crabworld': the spatial distribution of light in a tropical mudflat

Natural scene analysis has been extensively used to understand how the invariant structure of the visual environment may have shaped biological image processing strategies. This paper deals with four crucial, but hitherto largely neglected aspects of natural scenes: (1) the viewpoint of specific animals; (2) the fact that image statistics are not independent of the position within the visual field; (3) the influence of the direction of illumination on luminance, spectral and polarization contrast in a scene; and (4) the biologically relevant information content of natural scenes. To address these issues, I recorded the spatial distribution of light in a tropical mudflat with a spectrographic imager equipped with a polarizing filter in an attempt to describe quantitatively the visual environment of fiddler crabs. The environment viewed by the crabs has a distinct structure. Depending on the position of the sun, the luminance, the spectral composition, and the polarization characteristics of horizontal light distribution are not uniform. This is true for both skylight and for reflections from the mudflat surface. The high-contrast feature of the line of horizon dominates the vertical distribution of light and is a discontinuity in terms of luminance, spectral distribution and of image statistics. On a clear day, skylight intensity increases towards the horizon due to multiple scattering, and its spectral composition increasingly resembles that of sunlight. Sky-substratum contrast is highest at short wavelengths. I discuss the consequences of this extreme example of the topography of vision for extracting biologically relevant information from natural scenes.

Investigation of the ultrastructures and retinal arrangements of larval stomatopod eyes

Though the transparent apposition eyes of larval stomatopod crustaceans lack most of the unique retinal specializations known from their adult counterparts, increasing evidence suggests that these tiny pelagic organisms possess their own version of retinal complexity. In this paper, we examined the structural organization of larval eyes in six species of stomatopod crustaceans across three stomatopod superfamilies using transmission electron microscopy. The primary focus was to examine retinular cell arrangement of the larval eyes and characterize the presence of an eighth retinular cell (R8), which is typically responsible for UV vision in crustaceans. For all species investigated, we identified R8 photoreceptor cells positioned distal to the main rhabdom of R1-7 cells. This is the first evidence that R8 photoreceptor cells exist in larval stomatopod retinas, and among the first identified in any larval crustacean. Considering recent studies that identified UV sensitivity in larval stomatopods, we propose that this sensitivity is driven by this putative R8 photoreceptor cell. Additionally, we identified a potentially unique crystalline cone structure in each of the species examined, the function of which is still not understood.

Black eye syndrome and a systemic rickettsia-like organism in Alaskan Chionoecetes spp. crabs, including normal eyestalk microanatomy

A black eye syndrome (BES) was discovered in both captive and wild populations of Alaskan snow crabs Chionoecetes opilio and Tanner crabs C. bairdi. Field prevalences ranged from 0.37% (n = 594/161295) to 19.6% (n = 62/316) in snow crabs from the eastern Bering Sea and from 0.09% (n = 15/16638) to 0.7% (n = 133/18473) in Tanner crabs from the same trawl samples, with a slightly greater percentage (1.4%, n = 57/3945) in Tanner crabs from the Aleutian and Kodiak islands fisheries in the Gulf of Alaska. BES is not associated with crab mortality and has 2 distinct manifestations: abnormal black foci of internal eye pigment with no discernible histological lesions, which, in many cases, is followed by corneal shell disease with ulceration and distal eyestalk erosion. It is assumed for this study that these are early and late stages of BES that are somehow related. Our results suggest that early stages of abnormal pigmentation are noninfectious, possibly related to changing ocean conditions affecting crab endocrinology and neuropeptide control of secondary eye pigment. Potential light-induced photoreceptor damage of harvested crabs with dark-adapted eyes is another anthropogenic factor possibly contributing to the early changes in eye pigmentation. Normal eyestalk microanatomy specific for Chionoecetes spp. is provided as necessary baseline information for future studies. Early in the study, an unreported rickettsia-like organism (RLO) was discovered infecting dissected black eyestalks submitted for examination from 5 of 6 dead snow crabs, suggesting association with BES. Subsequent samples indicated the RLO was systemic, infected both black and normal-appearing eyestalks, and was unrelated to BES. However, the multiorgan infection and histopathology indicated the RLO could be a primary pathogen of snow crabs.

InSegtCone: interactive segmentation of crystalline cones in compound eyes

Background

Understanding the diversity of eyes is crucial to unravel how different animals use vision to interact with their respective environments. To date, comparative studies of eye anatomy are scarce because they often involve time-consuming or inefficient methods. X-ray micro-tomography (micro-CT) is a promising high-throughput imaging technique that enables to reconstruct the 3D anatomy of eyes, but powerful tools are needed to perform fast conversions of anatomical reconstructions into functional eye models.

Results

We developed a computing method named InSegtCone to automatically segment the crystalline cones in the apposition compound eyes of arthropods. Here, we describe the full auto-segmentation process, showcase its application to three different insect compound eyes and evaluate its performance. The auto-segmentation could successfully label the full individual shapes of 60-80% of the crystalline cones and is about as accurate and 250 times faster than manual labelling of the individual cones.

Conclusions

We believe that InSegtCone can be an important tool for peer scientists to measure the orientation, size and dynamics of crystalline cones, leading to the accurate optical modelling of the diversity of arthropod eyes with micro-CT.

Photoreceptors and diurnal variation in spectral sensitivity in the fiddler crab Gelasimus dampieri

Colour signals, and the ability to detect them, are important for many animals and can be vital to their survival and fitness. Fiddler crabs use colour information to detect and recognise conspecifics, but their colour vision capabilities remain unclear. Many studies have attempted to measure their spectral sensitivity and identify contributing retinular cells, but the existing evidence is inconclusive. We used electroretinogram (ERG) measurements and intracellular recordings from retinular cells to estimate the spectral sensitivity of Gelasimus dampieri and to track diurnal changes in spectral sensitivity. G. dampieri has a broad spectral sensitivity and is most sensitive to wavelengths between 420 and 460 nm. Selective adaptation experiments uncovered an ultraviolet (UV) retinular cell with a peak sensitivity shorter than 360 nm. The species' spectral sensitivity above 400 nm is too broad to be fitted by a single visual pigment and using optical modelling, we provide evidence that at least two medium-wavelength sensitive (MWS) visual pigments are contained within a second blue-green sensitive retinular cell. We also found a ∼25 nm diurnal shift in spectral sensitivity towards longer wavelengths in the evening in both ERG and intracellular recordings. Whether the shift is caused by screening pigment migration or changes in opsin expression remains unclear, but the observation shows the diel dynamism of colour vision in this species. Together, these findings support the notion that G. dampieri possesses the minimum requirement for colour vision, with UV and blue/green receptors, and help to explain some of the inconsistent results of previous research.

Light adaptation mechanisms in the eye of the fiddler crab Afruca tangeri

A great diversity of adaptations is found among animals with compound eyes and even closely related taxa can show variation in their light-adaptation strategies. A prime example of a visual system evolved to function in specific light environments is the fiddler crab, used widely as a model to research aspects of crustacean vision and neural pathways. However, questions remain regarding how their eyes respond to the changes in brightness spanning many orders of magnitude, associated with their habitat and ecology. The fiddler crab Afruca tangeri forages at low tide on tropical and semi-tropical mudflats, under bright sunlight and on moonless nights, suggesting that their eyes undergo effective light adaptation. Using synchrotron X-ray tomography, light and transmission electron microscopy and in vivo ophthalmoscopy, we describe the ultrastructural changes in the eye between day and night. Dark adaptation at dusk triggered extensive widening of the rhabdoms and crystalline cone tips. This doubled the ommatidial acceptance angles and increased microvillar surface area for light capture in the rhabdom, theoretically boosting optical sensitivity 7.4 times. During daytime, only partial dark-adaptation was achieved and rhabdoms remained narrow, indicating strong circadian control on the process. Bright light did not evoke changes in screening pigment distributions, suggesting a structural inability to adapt rapidly to the light level fluctuations frequently experienced when entering their burrow to escape predators. This should enable fiddler crabs to shelter for several minutes without undergoing significant dark-adaptation, their vision remaining effectively adapted for predator detection when surfacing again in bright light.

Parallel processing of polarization and intensity information in fiddler crab vision

Many crustaceans are sensitive to the polarization of light and use this information for object-based visually guided behaviors. For these tasks, it is unknown whether polarization and intensity information are integrated into a single-contrast channel, whereby polarization directly contributes to perceived intensity, or whether they are processed separately and in parallel. Using a novel type of visual display that allowed polarization and intensity properties of visual stimuli to be adjusted independently and simultaneously, we conducted behavioral experiments with fiddler crabs to test which of these two models of visual processing occurs. We found that, for a loom detection task, fiddler crabs process polarization and intensity information independently and in parallel. The crab's response depended on whichever contrast was the most salient. By contributing independent measures of visual contrast, polarization and intensity provide a greater range of detectable contrast information for the receiver, increasing the chance of detecting a potential threat.