Absorption Spectra Of Visual Pigments Research Articles

Parallel evolution of opsin visual pigments in hawkmoths by tuning of spectral sensitivities during transition from a nocturnal to a diurnal ecology.

Light environments differ dramatically between day and night. The transition between diurnal and nocturnal visual ecology has happened repeatedly throughout evolution in many species. However, the molecular mechanism underlying the evolution of vision in recent diurnal-nocturnal transition is poorly understood. Here, we focus on hawkmoths (Lepidoptera: Sphingidae) to address this question by investigating five nocturnal and five diurnal species. We performed RNA-sequencing analysis and identified opsin genes corresponding to the ultraviolet (UV), short-wavelength (SW) and long-wavelength (LW)-absorbing visual pigments. We found no significant differences in the expression patterns of opsin genes between the nocturnal and diurnal species. We then constructed the phylogenetic trees of hawkmoth species and opsins. The diurnal lineages had emerged at least three times from the nocturnal ancestors. The evolutionary rates of amino acid substitutions in the three opsins differed between the nocturnal and diurnal species. We found an excess number of parallel amino acid substitutions in the opsins in three independent diurnal lineages. The numbers were significantly more than those inferred from neutral evolution, suggesting that positive selection acted on these parallel substitutions. Moreover, we predicted the visual pigment absorption spectra based on electrophysiologically determined spectral sensitivity in two nocturnal and two diurnal species belonging to different clades. In the diurnal species, the LW pigments shift 10 nm towards shorter wavelengths, and the SW pigments shift 10 nm in the opposite direction. Taken together, our results suggest that parallel evolution of opsins may have enhanced the colour discrimination properties of diurnal hawkmoths in ambient light.

Behavioural red-light sensitivity in fish according to the optomotor response.

Various procedures have been adopted to investigate spectral sensitivity of animals, e.g. absorption spectra of visual pigments, electroretinography, optokinetic response, optomotor response (OMR) and phototaxis. The use of these techniques has led to various conclusions about animal vision. However, visual sensitivity should be evaluated consistently for a reliable comparison. In this study, we retrieved behavioural data of several fish species using a single OMR procedure and compared their sensitivities to near-infrared light. Besides cavefish that lack eyes, some species were not appropriate for the OMR test because they either stayed still or changed swimming direction frequently. Eight of 13 fish species tested were OMR positive. Detailed analyses using medaka, goldfish, zebrafish, guppy, stickleback and cichlid revealed that all the fish were sensitive to light at a wavelength greater than or equal to 750 nm, where the threshold wavelengths varied from 750 to 880 nm. Fish opsin repertoire affected the perception of red light. By contrast, the copy number of long-wavelength-sensitive (LWS) genes did not necessarily improve red-light sensitivity. While the duplication of LWS and other cone opsin genes that has occurred extensively during fish evolution might not aid increasing spectral sensitivity, it may provide some other advantageous ophthalmic function, such as enhanced spectral discrimination.

Effects of light environment during growth on the expression of cone opsin genes and behavioral spectral sensitivities in guppies(Poecilia reticulata).

BackgroundThe visual system is important for animals for mate choice, food acquisition, and predator avoidance. Animals possessing a visual system can sense particular wavelengths of light emanating from objects and their surroundings and perceive their environments by processing information contained in these visual perceptions of light. Visual perception in individuals varies with the absorption spectra of visual pigments and the expression levels of opsin genes, which may be altered according to the light environments. However, which light environments and the mechanism by which they change opsin expression profiles and whether these changes in opsin gene expression can affect light sensitivities are largely unknown. This study determined whether the light environment during growth induced plastic changes in opsin gene expression and behavioral sensitivity to particular wavelengths of light in guppies (Poecilia reticulata).ResultsIndividuals grown under orange light exhibited a higher expression of long wavelength-sensitive (LWS) opsin genes and a higher sensitivity to 600-nm light than those grown under green light. In addition, we confirmed that variations in the expression levels of LWS opsin genes were related to the behavioral sensitivities to long wavelengths of light.ConclusionsThe light environment during the growth stage alters the expression levels of LWS opsin genes and behavioral sensitivities to long wavelengths of light in guppies. The plastically enhanced sensitivity to background light due to changes in opsin gene expression can enhance the detection and visibility of predators and foods, thereby affecting survival. Moreover, changes in sensitivities to orange light may lead to changes in the discrimination of orange/red colors of male guppies and might alter female preferences for male color patterns.Electronic supplementary materialThe online version of this article (doi:10.1186/s12862-016-0679-z) contains supplementary material, which is available to authorized users.

Spectral absorption of visual pigments in stomatopod larval photoreceptors.

Larval stomatopod eyes appear to be much simpler versions of adult compound eyes, lacking most of the visual pigment diversity and photoreceptor specializations. Our understanding of the visual pigment diversity of larval stomatopods, however, is based on four species, which severely limits our understanding of stomatopod eye ontogeny. To investigate several poorly understood aspects of stomatopod larval eye function, we tested two hypotheses surrounding the spectral absorption of larval visual pigments. First, we examined a broad range of species to determine if stomatopod larvae generally express a single, spectral class of photoreceptor. Using microspectrophotometry (MSP) on larvae captured in the field, we found data which further support this long-standing hypothesis. MSP was also used to test whether larval species from the same geographical region express visual pigments with similar absorption spectra. Interestingly, despite occupation of the same geographical location, we did not find evidence to support our second hypothesis. Rather, there was significant variation in visual pigment absorption spectra among sympatric species. These data are important to further our understanding of larval photoreceptor spectral diversity, which is beneficial to ongoing investigations into the ontogeny, physiology, and molecular evolution of stomatopod eyes.Electronic supplementary materialThe online version of this article (doi:10.1007/s00359-015-1063-y) contains supplementary material, which is available to authorized users.

Contribution of a visual pigment absorption spectrum to a visual function: depth perception in a jumping spider.

Absorption spectra of visual pigments are adaptively tuned to optimize informational capacity in most visual systems. Our recent investigation of the eyes of the jumping spider reveals an apparent exception: the absorption characteristics of a visual pigment cause defocusing of the image, reducing visual acuity generally in a part of the retina. However, the amount of defocus can theoretically provide a quantitative indication of the distance of an object. Therefore, we proposed a novel mechanism for depth perception in jumping spiders based on image defocus. Behavioral experiments revealed that the depth perception of the spider depended on the wavelength of the ambient light, which affects the amount of defocus because of chromatic aberration of the lens. This wavelength effect on depth perception was in close agreement with theoretical predictions based on our hypothesis. These data strongly support the hypothesis that the depth perception mechanism of jumping spiders is based on image defocus.

Shortwave light filtration effect on spectral sensitivity of two shrimp populations of M. relicta (Mysida)

Microspectrophotometric measurements of screening granules in Mysis relicta eyes showed that most of the granules have xanthommatin spectra (7nmax 455 nm) with selective absorption of blue light. We calculated spectral sensitivity of M.relicta eyes using screening granules absorption spectra and visual pigment absorption spectra. According to our computations the calculated spectral sensitivity curve appears to be in a good correspondence with the real spectral sensitivity.

Modulation of the Absorption Maximum of Rhodopsin by Amino Acids in the C-terminus†

Vision begins when light is absorbed by visual pigments. It is commonly believed that the absorption spectra of visual pigments are modulated by interactions between the retinal and amino acids within or near 4.5 angstroms of the retinal in the transmembrane (TM) segments. However, this dogma has not been rigorously tested. In this study, we show that the retinal-opsin interactions extend well beyond the retinal binding pocket. We found that, although it is positioned outside of TM segments, the C-terminus of the rhodopsin in the rockfish longspine thornyhead (Sebastolobus altivelis) modulates its lambda(max) by interacting mainly with the last TM segment. Our results illustrate how amino acids in the C-terminus are likely to interact with the retinal. We anticipate our analyses to be a starting point for viewing the spectral tuning of visual pigments as interactions between the retinal and key amino acids that are distributed throughout the entire pigment.

The effect of elevated hydrostatic pressure on the spectral absorption of deep-sea fish visual pigments

The effect of hydrostatic pressure (0.1-54 MPa, equivalent to pressures experienced by fish from the ocean's surface to depths of ca. 5,400 m) on visual pigment absorption spectra was investigated for rod visual pigments extracted from the retinae of 12 species of deep-sea fish of diverse phylogeny and habitat. The wavelength of peak absorption (lambda(max)) was shifted to longer wavelengths by an average of 1.35 nm at 40 MPa (a pressure approximately equivalent to average ocean depth) relative to measurements made at one atmosphere (ca. 0.1 MPa), but with little evidence of a change in absorbance at the lambda(max). We conclude that previous lambda(max) measurements of deep-sea fish visual pigments, made at a pressure close to 0.1 MPa, provide a good indication of lambda(max) values at higher pressures when considering the ecology of vision in the deep-sea. Although not affecting the spectral sensitivity of the animal to any important degree, the observed shift in lambda(max) may be of interest in the context of understanding opsin-chromophore interaction and spectral tuning of visual pigments.

Absorption spectra of reconstituted visual pigments of a nocturnal prosimian, Otolemur crassicaudatus

Absorption spectra of visual pigments characterize animal vision. The association between absorption spectra and amino acid (aa) sequences of pigments has been well established for the middle- to-long-wave-sensitive (M/LWS) class of cone visual pigments of vertebrates, known as the “five-sites” rule where amino acid residues at the 180th, 197th, 277th, 285th, and 308th sites mostly determine the spectra. For primate M/LWS pigments, however, applicability of the rule is not clear because of the scarcity of absorbance data collected directly from purified pigments. In particular, no prosimian pigment has been examined in vitro. In this study, we reconstituted visual pigments of a nocturnal prosimian, the greater galago ( Otolemur crassicaudatus), which has the M/LWS cone and the rod visual pigments in its retina. The five residues of the galago M/LWS pigment are Ala, His, Tyr, Ala, and Ala, respectively, and its peak absorption spectra ( λ max) was measured to be 539 nm, which is virtually identical to the expected value from the rule (538 nm), showing that the five-sites rule holds for this prosimian. The λ max of the rod visual pigment was measured as 502 nm. Accurate estimate of λ max values is essential in establishing the molecular basis of visual pigment evolution.

Molecular evolution of color vision in vertebrates

Visual systems of vertebrates exhibit a striking level of diversity, reflecting their adaptive responses to various color environments. The photosensitive molecules, visual pigments, can be synthesized in vitro and their absorption spectra can be determined. Comparing the amino acid sequences and absorption spectra of various visual pigments, we can identify amino acid changes that have modified the absorption spectra of visual pigments. These hypotheses can then be tested using the in vitro assay. This approach has been a powerful tool in elucidating not only the molecular bases of color vision, but the processes of adaptive evolution at the molecular level.

Evidence for a two pigment visual system in the fiddler crab, Uca thayeri.

Intraocular recordings were made from the eyestalks of dark-adapted fiddler crabs (Uca thayeri) during presentation of monochromatic light flashes of different wavelengths and intensities. Two types of signals were recorded in different experiments: slow potentials (electroretinogram) and fast potentials (spikes). The latter were also recorded in the presence of a continuous green or red adapting light. The resulting visual spectral-sensitivity curves, when fitted to rhodopsin-based visual pigment absorption spectra (from Dartnall nomograms), indicated the presence of two visual pigments, one with an absorption maximum near 430 nm, and the other with a peak absorption between 500 nm and 540 nm. The data also provided evidence for some differential bleaching of the pigments in the presence of a colored adapting light, but most of the adaptation effect was probably due to changes in screening pigment and neural desensitization or inhibition. These two observations suggest that an adequate substrate for color vision may exist in this and other species of fiddler crabs. The electroretinogram and spike-recording methods produced similar visual-sensitivity data, suggesting that latter technique, a much more efficient way of collecting data that is physiologically relevant, may be the method of choice for determining spectral sensitivity in crustaceans.

Molecular evolution of color vision of zebra finch

We have isolated and sequenced the RH1Tg, RH2Tg, SWS2Tg, and LWSTg opsin cDNAs from zebra finch retinas. Upon binding to 11-cis-retinal, these opsins regenerate the corresponding photosensitive molecules, visual pigments. The absorption spectra of visual pigments have a broad bell shape, with the peak being called λmax. Previously, SWS1Tg opsin cDNA was isolated from zebra finch retinal RNA, expressed in cultured COS1 cells, reconstituted with 11-cis-retinal, and the λmax of the resulting visual pigment was shown to be 359nm. Here, the λmax values of the RH1Tg, RH2Tg, SWS2Tg, and LWSTg pigments are determined to be 501, 505, 440, and 560nm, respectively. Molecular evolutionary analyses suggest that specific amino acid replacements in the SWS1 and SWS2 pigments, resulting from accelerated evolution, must have been responsible for their functional divergences among the avian pigments.

Multiple visual pigments in a photoreceptor of the salamander retina.

Although a given retina typically contains several visual pigments, each formed from a retinal chromophore bound to a specific opsin protein, single photoreceptor cells have been thought to express only one type of opsin. This design maximizes a cell's sensitivity to a particular wavelength band and facilitates wavelength discrimination in retinas that process color. We report electrophysiological evidence that the ultraviolet-sensitive cone of salamander violates this rule. This cell contains three different functional opsins. The three opsins could combine with the two different chromophores present in salamander retina to form six visual pigments. Whereas rods and other cones of salamander use both chromophores, they appear to express only one type of opsin per cell. In visual pigment absorption spectra, the bandwidth at half-maximal sensitivity increases as the pigment's wavelength maximum decreases. However, the bandwidth of the UV-absorbing pigment deviates from this trend; it is narrow like that of a red-absorbing pigment. In addition, the UV-absorbing pigment has a high apparent photosensitivity when compared with that of red- and blue-absorbing pigments and rhodopsin. These properties suggest that the mechanisms responsible for spectrally tuning visual pigments separate two absorption bands as the wavelength of maximal sensitivity shifts from UV to long wavelengths.

Ultraviolet photoreception in carp: Microspectrophotometry and behaviorally determined action spectra

This study demonstrates correlations between u.v. sensitivity and microspectrophotometric absorption spectra determined sequentially for the same group of individuals. We used the heart-rate conditioning technique to measure spectral sensitivity of carp, a species known to have u.v.-sensitive photoreceptors. Mean spectral sensitivity ( n = 3) determined with a spectrally-broad background (450 nm long pass filter) revealed a small but consistent u.v. peak (λ max of 380 nm) in addition to the other long wavelength peaks. An intense blue-green background (490 nm) produced a more prominent u.v. peak (λ max of 400 nm) when a 450 nm longpass filter was added to the background. Microspectrophotometric measurements of u.v.-sensitive photoreceptors from one individual, which belonged to the group used in the spectral sensitivity experiments, revealed an average λ max of 377.5 nm (SD ± 4.5 nm, n = 5 cells). Bleaching and dichroic measurements of these receptors ensured that we were examining typical vertebrate visual pigments and not stable photoproducts. The mean spectral sensitivity points were compared with the u.v. and blue-sensitive visual pigment absorption spectra. A linear subtractive model and ocular media absorption were used in this comparison for the various photic conditions used in the heart-rate conditioning experiments. The model successfully described the sensitivity of the test fish in two cases but in a third case there was some discrepancy. The model generated curve was broader than the spectral sensitivity of the u.v.-sensitive cone mechanism on the shortwave side even though the ocular media corrections had been accounted for.

Is the white eye of insect eye-color mutants really white?

1. Spectral sensitivity curves (SSCs) of (a) the whole eye and peripheral photoreceptors R1–6 were recorded in wild-type flies and chalky mutants of Calliphora, and (b) the whole eye of Drosophila, wild type and mutant white. Our spectrosensitometer provided good resolution and accuracy. 2. A vibrational fine structure of the SSC in the ultra-violet spectral range was clearly resolved in all the genotypes studied (Fig. 1). 3. In the visible spectral range, the SSCs of white-eyed mutants appeared to be significantly narrower than the absorption spectrum of the template visual pigments (Fig. 2). The bandwidth ratios (wild type: visual pigment: white-eyed mutant) were as follows: 111±10:102:95±4nm and 114±14:102:93±7 nm in Calliphora whole eye and cells R1–6, respectively; and 118±6:100:97±2 nm in the whole eye of Drosophila (Fig. 3). 4. Long-wave portions of SSCs in mutants showed a good fit with those of the absorption spectrum of visual pigments: P490 for the whole eye, P487 for receptors R1-6 of chalky mutants of Calliphora, and P478 for the whole eye of Drosophila. 5. The narrowing of the SSCs compared with the absorption spectrum of the template visual pigment is believed to be due to the presence of hypothetical blue-absorbing pigments in the eye media.

Blue light hazard in rat

Rats have been extensively used in light damage studies. Retinal damage threshold for white light were found at 1–10 J/cm 2, and the action spectrum resembled the absorption spectrum of visual pigment. We wished to answer the question whether a different class of light damage, the “blue light hazard”, with white light damage thresholds at about 300 J/cm 2, and an action spectrum peaking in the ultra-violet, could also be demonstrated in rat. To that purpose 5 deg patches of retina were exposed to white xenon light with exposure times between 10 sec and 1 hr. We found that for funduscopic threshold damage the product of irradiance and exposure time was constant at a level of 315 J/cm 2. Thereafter, the action spectrum was measured by exposing rat eyes to narrow band spectral lights. Threshold irradiant dose ranged from 4 J/cm 2 at 379 nm to 2000 J/cm 2 at 559 nm. Thus, susceptibility for damage sharply increased towards the ultra-violet, just like in earlier monkey studies. We conclude that in similar experimental conditions susceptibility to photic injury in rat is comparable to that in primates. Rat is the first species for which two different action spectra of photochemical damage have been established.

Application of an invariant spectral form to the visual pigments of crustaceans: Implications regarding the binding of the chromophore

Visual pigment absorption spectra were measured in single photoreceptors of a stomatopod, a crayfish, a hermit crab, and five species of brachyuran crab. All fitted a Mansfield (1985) invariant form for visual pigment, the form also fitted by vertebrate retinal-based visual pigments. This is consistent with a theoretical model based on the structure of visual pigment molecules (Greenberg et al., 1975; Honig et al.,1976) which predicts that spectral bandwidth decreases as λ max increases. The conformation to the invariant form implies that for any given chromophore bandwidth times λ max is a constant.

Gaussian expressions for the absorption spectra of visual pigments

Gaussian expressions for the absorption spectra of visual pigments

Spectral sensitivity of color-blind observers and the cone photopigments

A comparison was made between Dartnall's standard shape for visual pigments and the spectral sensitivities of the short-, middle-, and long-wavelength sensitive cone receptor mechanisms of man Data from blue monocone monochromats, protanopes, and deuteranopes were chosen as reliable estimates of each of the three classes of cone sensitivities The shortwavelength sensitive mechanism fits the standard shape The middle- and long-wavelength sensitive mechanisms have the same shape on a wavenumber axis but do not fit Dartnall's standard shape for visual pigments The shape of the middle- and long-wavelength sensitive mechanisms also describes some other published absorption spectra of visual pigments with λ max > 520 nm , notably the lodopsins found in birds.

Sensitive low-light-level microspectrophotometer: detection of photosensitive pigments of retinal cones.

A microspectrophotometer of exceptional sensitivity has been constructed to record absorption spectra of visual pigments in single cells using minimum light. With this equipment, pigments of individual cones have been recorded in regions of less than 1 μ radius, with minimum bleaching. The instrument is simple and flexible in design, and uses commercially available components throughout. This paper reviews some general design considerations, the character and performance of our equipment, and some of the results obtained with retinal cones.