Short-wavelength Sensitivity Research Articles

Spectral sensitivity of cone photoreceptors and opsin expression in two colour-divergent lineages of the lizard Ctenophorus decresii.

Intraspecific differences in sensory perception are rarely reported but may occur when a species range extends across varying sensory environments, or there is coevolution between the sensory system and a varying signal. Examples in colour vision and colour signals are rare in terrestrial systems. The tawny dragon lizard Ctenophorus decresii is a promising candidate for such intraspecific variation, because the species comprises two geographically and genetically distinct lineages in which throat colour (a social signal used in intra- and inter-specific interactions) is locally adapted to the habitat and differs between lineages. Male lizards from the southern lineage have UV-blue throats, whereas males from the northern lineage are polymorphic with four discrete throat colours that all show minimal UV reflectance. Here, we determine the cone photoreceptor spectral sensitivities and opsin expression of the two lineages, to test whether they differ, particularly in the UV wavelengths. Using microspectrophotometry on retinal cone photoreceptors, we identified a long-wavelength-sensitive (LWS) visual pigment, a 'short' and 'long' medium-wavelength-sensitive (MWS) pigment and a short-wavelength-sensitive (SWS) pigment, all of which did not differ in λmax between lineages. Through transcriptome analysis of opsin genes we found that both lineages express four cone opsin genes, including the SWS1 opsin with peak sensitivity in the UV range, and that amino acid sequences did not differ between lineages with the exception of a single leucine to valine substitution in the RH2 opsin. Counts of yellow and transparent oil droplets associated with LWS+MWS and SWS+UVS cones, respectively, showed no difference in relative cone proportions between lineages. Therefore, contrary to predictions, we find no evidence of differences between lineages in single cone photoreceptor spectral sensitivity or opsin expression. However, we confirm the presence of four single cone classes, suggesting tetrachromacy in C. decresii, and we also provide the first evidence of UV sensitivity in agamid lizards.

Spectral Sensitivity Modeling and Nighttime Scene Brightness Perception

ABSTRACTBrightness perception under different light sources is an important visual response, because it is related to perceptions of safety. A growing number of studies have been conducted to assess perceptions of scene brightness under light sources differing in spectral content, including results consistent with a role of melanopsin-containing, intrinsically photosensitive retinal ganglion cells in scene brightness. Data from recent studies of scene brightness perception at light levels experienced under nighttime driving conditions are used to compare different models of brightness perception. The data support a role of increased short-wavelength sensitivity for scene brightness perception and a provisional spectral sensitivity model that takes into account the possible influence of melanopsin-containing, intrinsically photoreceptive retinal ganglion cells is suggested as a basis for further investigation. The implications of such a model on brightness perception under several light sources used in transportation lighting are described.

Spectral tuning in vertebrate short wavelength-sensitive 1 (SWS1) visual pigments: can wavelength sensitivity be inferred from sequence data?

The molecular mechanisms underlying the enormous diversity of visual pigment wavelength sensitivities found in nature have been the focus of many molecular evolutionary studies, with particular attention to the short wavelength-sensitive 1 (SWS1) visual pigments that mediate vision in the ultraviolet to violet range of the electromagnetic spectrum. Over a decade of study has revealed that the remarkable extension of SWS1 absorption maxima (λ max ) into the ultraviolet occurs through a deprotonation of the Schiff base linkage of the retinal chromophore, a mechanism unique to this visual pigment type. In studies of visual ecology, there has been mounting interest in inferring visual sensitivity at short wavelengths, given the importance of UV signaling in courtship displays and other behaviors. Since experimentally determining spectral sensitivities can be both challenging and time-consuming, alternative strategies such as estimating λ max based on amino acids at sites known to affect spectral tuning are becoming increasingly common. However, these estimates should be made with knowledge of the limitations inherent in these approaches. Here, we provide an overview of the current literature on SWS1 site-directed mutagenesis spectral tuning studies, and discuss methodological caveats specific to the SWS1-type pigments. We focus particular attention on contrasting avian and mammalian SWS1 spectral tuning mechanisms, which are the best studied among vertebrates. We find that avian SWS1 visual pigment spectral tuning mechanisms are fairly consistent, and therefore more predictable in terms of wavelength absorption maxima, whereas mammalian pigments are not well suited to predictions of λ max from sequence data alone.

Photoreceptor topography and spectral sensitivity in the common brushtail possum (Trichosurus vulpecula).

Marsupials are believed to be the only non-primate mammals with both trichromatic and dichromatic color vision. The diversity of color vision systems present in marsupials remains mostly unexplored. Marsupials occupy a diverse range of habitats, which may have led to considerable variation in the presence, density, distribution, and spectral sensitivity of retinal photoreceptors. In this study we analyzed the distribution of photoreceptors in the common brushtail possum (Trichosurus vulpecula). Immunohistochemistry in wholemounts revealed three cone subpopulations recognized within two spectrally distinct cone classes. Long-wavelength sensitive (LWS) single cones were the largest cone subgroup (67-86%), and formed a weak horizontal visual streak (peak density 2,106 ± 435/mm2) across the central retina. LWS double cones were strongly concentrated ventrally (569 ± 66/mm2), and created a "negative" visual streak (134 ± 45/mm2) in the central retina. The strong regionalization between LWS cone topographies suggests differing visual functions. Short-wavelength sensitive (SWS) cones were present in much lower densities (3-10%), mostly located ventrally (179 ± 101/mm2). A minority population of cones (0-2.4%) remained unlabeled by both SWS- and LWS-specific antibodies, and may represent another cone population. Microspectrophotometry of LWS cone and rod visual pigments shows peak spectral sensitivities at 544 nm and 500 nm, respectively. Cone to ganglion cell convergences remain low and constant across the retina, thereby maintaining good visual acuity, but poor contrast sensitivity during photopic vision. Given that brushtail possums are so strongly nocturnal, we hypothesize that their acuity is set by the scotopic visual system, and have minimized the number of cones necessary to serve the ganglion cells for photopic vision.

Diurnal Spectral Sensitivity of the Acute Alerting Effects of Light

Previous studies have demonstrated short-wavelength sensitivity for the acute alerting response to nocturnal light exposure. We assessed daytime spectral sensitivity in alertness, performance, and waking electroencephalogram (EEG). Between-subjects (n = 8 per group). Inpatient intensive physiologic monitoring unit. Sixteen healthy young adults (mean age ± standard deviation = 23.8 ± 2.7 y). Equal photon density exposure (2.8 × 10(13) photons/cm(2)/s) to monochromatic 460 nm (blue) or 555 nm (green) light for 6.5 h centered in the middle of the 16-h episode of wakefulness during the biological day. Results were compared retrospectively to 16 individuals who were administered the same light exposure during the night. Daytime and nighttime 460-nm light exposure significantly improved auditory reaction time (P < 0.01 and P < 0.05, respectively) and reduced attentional lapses (P < 0.05), and improved EEG correlates of alertness compared to 555-nm exposure. Whereas subjective sleepiness ratings did not differ between the two spectral conditions during the daytime (P > 0.05), 460-nm light exposure at night significantly reduced subjective sleepiness compared to 555-nm light exposure at night (P < 0.05). Moreover, nighttime 460-nm exposure improved alertness to near-daytime levels. The alerting effects of short-wavelength 460-nm light are mediated by counteracting both the circadian drive for sleepiness and homeostatic sleep pressure at night, but only via reducing the effects of homeostatic sleep pressure during the day.

Sunscreen for Fish: Co-Option of UV Light Protection for Camouflage

Many animals change their body pigmentation according to illumination of their environment. In aquatic vertebrates, this reaction is mediated through aggregation or dispersion of melanin-filled vesicles (melanosomes) in dermal pigment cells (melanophores). The adaptive value of this behavior is usually seen in camouflage by allowing the animal to visually blend into the background. When exposed to visible light from below, however, dark-adapted zebrafish embryos at the age of 2 days post fertilization (dpf) surprisingly display dispersal instead of aggregation of melanosomes, i.e. their body coloration becomes dark on a bright background. Melanosomes of older embryos and early larvae (3–5 dpf) on the other hand aggregate as expected under these conditions. Here we provide an explanation to this puzzling finding: Melanosome dispersion in larvae 3 dpf and older is efficiently triggered by ultraviolet (UV) light, irrespective of the visual background, suggesting that the extent of pigmentation is a trade-off between threats from predation and UV irradiation. The UV light-induced dispersion of melanosomes thereby is dependent on input from retinal short wavelength-sensitive (SWS) cone photoreceptors. In young embryos still lacking a functional retina, protection from UV light predominates, and light triggers a dispersal of melanosomes via photoreceptors intrinsic to the melanophores, regardless of the actual UV content. In older embryos and early larvae with functional retinal photoreceptors in contrast, this light-induced dispersion is counteracted by a delayed aggregation in the absence of UV light. These data suggest that the primary function of melanosome dispersal has evolved as a protective adaption to prevent UV damage, which was only later co-opted for camouflage.

The importance of ultraviolet and near-infrared sensitivity for visual discrimination in two species of lacertid lizards.

Male and female Lacertid lizards often display conspicuous coloration that is involved in intraspecific communication. However, visual systems of Lacertidae have rarely been studied and the spectral sensitivity of their retinal photoreceptors remains unknown. Here, we characterise the spectral sensitivity of two Lacertid species from contrasting habitats: the wall lizard Podarcis muralis and the common lizard Zootoca vivipara. Both species possess a pure-cone retina with one spectral class of double cones and four spectral classes of single cones. The two species differ in the spectral sensitivity of the LWS cones, the relative abundance of UVS single cones (potentially more abundant in Z. vivipara) and the coloration of oil droplets. Wall lizards have pure vitamin A1-based photopigments, whereas common lizards possess mixed vitamin A1 and A2 photopigments, extending spectral sensitivity into the near infrared, which is a rare feature in terrestrial vertebrates. We found that spectral sensitivity in the UV and near infrared improves discrimination of small variations in throat coloration among Z. vivipara. Thus, retinal specialisations optimise chromatic resolution in common lizards, indicating that the visual system and visual signals might co-evolve.

Influence of Spectral Power Distribution on Scene Brightness at Different Light Levels

ABSTRACTExterior lighting has multiple objectives. Brightness perception is a relevant parameter for outdoor lighting because it is correlated with perceptions of safety and security. Understanding the influence of the spectral characteristics of lighting to scene brightness perception is important in order to devise exterior lighting specifications that support perceptions of safety and security in exterior lighted environments, as well as to optimize light source technologies to account for these factors. A study of scene brightness perception under different light levels and spectral power distributions was conducted to assess whether scene brightness perception exhibited increased short-wavelength spectral sensitivity as a function of increasing light level. The results confirm that a successful model of spectral sensitivity for scene brightness perception should incorporate a shift in short-wavelength sensitivity like the one investigated in the present study.

A Phe-rich region in short-wavelength sensitive opsins is responsible for their aggregation in the absence of 11-cis-retinal

Human blue and mouse S-opsin are prone to aggregation in the absence of 11-cis-retinal, which underlie the rapid cone degeneration in human patients and animal models of Leber congenital amaurosis (LCA). By in silico analysis and domain swapping experiments, we show that a Phe-rich region in short-wavelength sensitive (SWS) opsins, but not in medium/long-wavelength sensitive opsins, is responsible for SWS opsin aggregation. Mutagenesis studies suggest that Phe residues in this region are critical in mediating protein aggregation. Fusing the Phe-rich region of SWS opsins to GFP causes the latter to aggregate. Our findings suggest that new therapeutics can be designed to disrupt the Phe-rich region in preventing cone degeneration due to S-opsin aggregation in LCA.

Material Dependence of Metal Grating on SOI Photodiode for Enhanced Quantum Efficiency

Material dependence of line-and-space metal grating among gold, silver, and aluminum, is experimentally investigated for a 100-nm-thick silicon-on-insulator p-n junction photodiode in terms of enhanced light sensitivity. It is found that light sensitivity in the visible long-wavelength region is enhanced with any grating material, and the peak wavelengths, which are determined by the grating period, are not much affected by the material. The relationship between the peak wavelength and the grating period is explained theoretically. The results indicate that the grating material can be selected from these materials by taking into account the short-wavelength sensitivity and compatibility with applications.

The relationship between foveal short-wavelength-sensitive visual function and macular pigment optical density in the ageing age

To investigate the role of macular pigment in preserving foveal short-wavelength-sensitive (SWS) visual function in the ageing eye orientation identification acuity was measured in the fovea and at 12° eccentricity (nasal visual field) under SWS-cone isolating conditions in 73 participants (aged 20-71). Macular pigment optical density (MPOD) was measured at 0.5° eccentricity from the foveal centre using a heterochromatic flicker photometry (HFP) based instrument. MPOD was not significantly related to age but reduced SWS orientation identification acuity was associated with increasing age in the fovea and at 12° eccentricity. The rate at which foveal acuity changed in relation to acuity at 12° with increasing age was not significantly related to macular pigment levels. These findings do not support the hypothesis that higher macular pigment levels protect S-cone mediated foveal visual function in the ageing eye.

Nocturnal Light Environments Influence Color Vision and Signatures of Selection on the OPN1SW Opsin Gene in Nocturnal Lemurs

Although loss of short-wavelength-sensitive (SWS) cones and dichromatic color vision in mammals has traditionally been linked to a nocturnal lifestyle, recent studies have identified variation in selective pressure for the maintenance of the OPN1SW opsin gene (and thus, potentially dichromacy) among nocturnal mammalian lineages. These studies hypothesize that purifying selection to retain SWS cones may be associated with a selective advantage for nocturnal color vision under certain ecological conditions. In this study, we explore the effect of nocturnal light environment on OPN1SW opsin gene evolution in a diverse sample of nocturnal lemurs (106 individuals, 19 species, and 5 genera). Using both phylogenetic and population genetic approaches, we test whether species from closed canopy rainforests, which are impoverished in short-wavelength light, have experienced relaxed selection compared with species from open canopy forests. We identify clear signatures of differential selection on OPN1SW by habitat type. Our results suggest that open canopy species generally experience strong purifying selection to maintain SWS cones. In contrast, closed canopy species experience weaker purifying selection or a relaxation of selection on OPN1SW. We also found evidence of nonfunctional OPN1SW genes in all Phaner species and in Cheirogaleus medius, implying at least three independent losses of SWS cones in cheirogaleids. Our results suggest that the evolution of color vision in nocturnal lemurs has been influenced by nocturnal light environment.

Light-dependent Structural Change of Chicken Retinal Cryptochrome4

Animals have several classes of cryptochromes (CRYs), some of which function as core elements of circadian clockwork, circadian photoreceptors, and/or light-dependent magnetoreceptors. In addition to the circadian clock genes Cry1 and Cry2, nonmammalian vertebrates have the Cry4 gene, the molecular function of which remains unknown. Here we analyzed chicken CRY4 (cCRY4) expression in the retina with in situ hybridization and found that cCRY4 was likely transcribed in the visual pigment cells, cells in the inner nuclear layer, and retinal ganglion cells. We further developed several monoclonal antibodies to the carboxyl-terminal extension of cCRY4 and localized cCRY4 protein with immunohistochemistry. Consistent with the results of in situ hybridization, cCRY4 immunoreactivity was found in visual pigment cells and cells located at the inner nuclear layer and the retinal ganglion cell layer. Among the antibodies, one termed C1-mAb had its epitope within the carboxyl-terminal 14-amino acid sequence (QLTRDDADDPMEMK) and associated with cCRY4 in the retinal soluble fraction more strongly in the dark than under blue light conditions. Immunoprecipitation experiments under various light conditions indicated that cCRY4 from the immunocomplex formed in the dark dissociated from C1-mAb during blue light illumination as weak as 25 μW/cm(2) and that the release occurred with not only blue but also near UV light. These results suggest that cCRY4 reversibly changes its structure within the carboxyl-terminal region in a light-dependent manner and operates as a photoreceptor or magnetoreceptor with short wavelength sensitivity in the retina.

A case of bilateral, acquired, and acute dysfunction of short-wavelength-sensitive cone systems

To report a case of bilateral, acquired, and acute dysfunction of short-wavelength-sensitive (SWS) cone systems. The case was a healthy 39-year-old man. He noticed sudden onset of bilateral abnormal color vision. Ophthalmic examinations revealed normal fundi in both eyes. Farnsworth panel D-15 test and Farnsworth-Munsell 100-hue test showed tritanopia. White-on-white static perimetry showed no abnormality; however, blue-on-yellow static perimetry detected remarkably reduced sensitivity at the lower visual field in both eyes. ISCEV-standard full-field electroretinograms (ERGs) were normal; however, blue-on-yellow ERGs showed reduced amplitude of b-wave that was derived from SWS cone systems in both eyes. He was observed for 1 year, and no improvement in color vision was found during the observation. This is a unique case which showed bilateral, acquired, and acute dysfunction of SWS cone systems. The cause of the acquired tritanopia remains to be known.

High sensitivity to short wavelengths in a lizard and implications for understanding the evolution of visual systems in lizards

Progress in developing animal communication theory is frequently constrained by a poor understanding of sensory systems. For example, while lizards have been the focus of numerous studies in visual signalling, we only have data on the spectral sensitivities of a few species clustered in two major clades (Iguania and Gekkota). Using electroretinography and microspectrophotometry, we studied the visual system of the cordylid lizard Platysaurus broadleyi because it represents an unstudied clade (Scinciformata) with respect to visual systems and because UV signals feature prominently in its social behaviour. The retina possessed four classes of single and one class of double cones. Sensitivity in the ultraviolet region (UV) was approximately three times higher than previously reported for other lizards. We found more colourless oil droplets (associated with UV-sensitive (UVS) and short wavelength-sensitive (SWS) photoreceptors), suggesting that the increased sensitivity was owing to the presence of more UVS photoreceptors. Using the Vorobyev-Osorio colour discrimination model, we demonstrated that an increase in the number of UVS photoreceptors significantly enhances a lizard's ability to discriminate conspecific male throat colours. Visual systems in diurnal lizards appear to be broadly conserved, but data from additional clades are needed to confirm this.

Laminated grid solar cells (LGCells) on multicrystalline silicon. Application of atomic hydrogen treatment

For the first time, solar cells of laminated grid cell (LGCell) design are fabricated on multicrystalline nontextured silicon (mc-Si). An efficiency of 15.9% is achieved. The effect of (n + pp +)-mc-Si structure treatment by atomic hydrogen generated by a hot filament and microwave plasma is studied. Hydrogenation improves the parameters describing the dependence of the open-circuit voltage on the radiation intensity and the long-wavelength (λ = 1000 nm) sensitivity of the solar cell by 10–20%, which indicates that defects in mc-Si are passivated. Hydrogenation of the emitter side results in an increase in the series resistance of the solar cell, a decrease in the short-wavelength (λ = 400 nm) sensitivity by 30–35%, and the appearance of an oxygen peak in the energy-dispersive spectra (EDS). These effects are eliminated by fine etching of the emitter.

Testing a provisional model of scene brightness with and without objects of different colours

A provisional model of brightness perception for illuminated outdoor scenes was recently proposed based upon a combination of photopic and short-wavelength cone spectral sensitivities, where short-wavelength cone sensitivity increases with radiance. An experiment was undertaken to determine whether coloured objects within the illuminated scenes affected overall scene brightness perception and, in so doing, to provide a test of the provisional model. The results suggest that overall scene brightness perceptions are, for the range of light sources and light levels selected, consistent with the provisional model and that scene brightness perception is independent of object colours within the illuminated scenes.

Spectral modulation attenuates molecular, endocrine, and neurobehavioral disruption induced by nocturnal light exposure

The human eye serves distinctly dual roles in image forming (IF) and non-image-forming (NIF) responses when exposed to light. Whereas IF responses mediate vision, the NIF responses affect various molecular, neuroendocrine, and neurobehavioral variables. NIF responses can have acute and circadian phase-shifting effects on physiological variables. Both the acute and phase-shifting effects induced by photic stimuli demonstrate short-wavelength sensitivity peaking ≈450-480 nm. In the current study, we examined the molecular, neuroendocrine, and neurobehavioral effects of completely filtering (0% transmission) all short wavelengths <480 nm and all short wavelengths <460 nm or partially filtering (~30% transmission) <480 nm from polychromatic white light exposure between 2000 and 0800 in healthy individuals. Filtering short wavelengths <480 nm prevented nocturnal light-induced suppression of melatonin secretion, increased cortisol secretion, and disrupted peripheral clock gene expression. Furthermore, subjective alertness, mood, and errors on an objective vigilance task were significantly less impaired at 0800 by filtering wavelengths <480 nm compared with unfiltered nocturnal light exposure. These changes were not associated with significantly increased sleepiness or fatigue compared with unfiltered light exposure. The changes in molecular, endocrine, and neurobehavioral processes were not significantly improved by completely filtering <460 nm or partially filtering <480 nm compared with unfiltered nocturnal light exposure. Repeated light-dark cycle alterations as in rotating nightshifts can disrupt circadian rhythms and induce health disorders. The current data suggest that spectral modulation may provide an effective method of regulating the effects of light on physiological processes.

Effects of ageing on postreceptoral short-wavelength gain control: Transient tritanopia increases with age

We investigated the effect of ageing on the neural gain control in the short-wavelength opponent channel. In order to tackle specifically postreceptoral changes, we determined the effect of ageing on transient tritanopia, a paradoxical and transient reduction of short-wavelength sensitivity after the presentation of a long-wavelength adapting light. The results demonstrate an unexpected and significant increase of transient tritanopia with age, which cannot be explained by a general decline of short-wave sensitivity or the selective reduction of retinal illumination. Instead, our data imply that ageing affects also short-wavelength gain control at the site of chromatic opponency or beyond. Age-related changes of adaptation processes should therefore be considered an important factor influencing the visual performances of the elderly.

Phylogenetic analyses in cetacean species of the family Delphinidae using a short wavelength sensitive opsin gene sequence

The short wavelength sensitive (SWS) opsin gene is expected to contain informative sites for understanding the speciation of the family Delphinidae, because it is not functional in cetaceans. We determined partial SWS gene sequences from 15 delphinid species of 12 genera and from harbor porpoise for comparison. We found a 39-bp insertion that was shared by six species (the insertion group: Delphinus delphis, Delphinus capensis, Stenella longirostris, Stenella coeruleoalba, Lagenodelphis hosei, and Sousa chinensis) and common base substitutions shared by eight species (Stenella frontalis, Tursiops truncatus, and six species of the insertion group). As these insertions and substitutions are not found in the other seven delphinids or in the cloven-hoofed mammals (which are close to cetaceans), it is suggested that these eight species are more closely related to each other than to the other species. This hypothesis is supported by phylogenetic analyses. The eight species with the substitutions formed a clade containing two sister clades, one consisting of the insertion group and the other consisting of the two other species, in both neighbor-joining and Bayes analyses. Phylogenetic analyses also showed that Lissodelphis borealis and Lagenorhynchus obliquidens are closely related and that their common ancestor diverged from the others at an early stage of delphinid evolution.