The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform
Nathan S Hart - One of the best experts on this subject based on the ideXlab platform.
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microspectrophotometry of Visual Pigments and oil droplets in a marine bird the wedge tailed shearwater puffinus pacificus topographic variations in photoreceptor spectral characteristics
The Journal of Experimental Biology, 2004Co-Authors: Nathan S HartAbstract:Microspectrophotometric examination of the retina of a procellariiform marine bird, the wedge-tailed shearwater Puffinus pacificus, revealed the presence of five different types of vitamin A(1)-based Visual Pigment in seven different types of photoreceptor. A single class of rod contained a medium-wavelength sensitive Visual Pigment with a wavelength of maximum absorbance (lambda(max)) at 502 nm. Four different types of single cone contained Visual Pigments maximally sensitive in either the violet (VS, lambda(max) 406 nm), short (SWS, lambda(max) 450 nm), medium (MWS, lambda(max) 503 nm) or long (LWS, lambda(max) 566 nm) spectral ranges. In the peripheral retina, the SWS, MWS and LWS single cones contained Pigmented oil droplets in their inner segments with cut-off wavelengths (lambda(cut)) at 445 (C-type), 506 (Y-type) and 562 nm (R-type), respectively. The VS Visual Pigment was paired with a transparent (T-type) oil droplet that displayed no significant absorption above at least 370 run. Both the principal and accessory members of the double cone pair contained the same 566 nm lambda(max) Visual Pigment as the LWS single cones but only the principal member contained an oil droplet, which had a lambda(cut) at 413 nm. The retina had a horizontal band or 'Visual streak' of increased photoreceptor density running across the retina approximately 1.5 mm dorsal to the top of the pecten. Cones in the centre of the horizontal streak were smaller and had oil droplets that were either transparent/colourless or much less Pigmented than at the periphery. It is proposed that the reduction in cone oil droplet Pigmentation in retinal areas associated with high Visual acuity is an adaptation to compensate for the reduced photon capture ability of the narrower photoreceptors found there. Measurements of the spectral transmittance of the ocular media reveal that wavelengths down to at least 300 nm would be transmitted to the retina.
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the Visual ecology of avian photoreceptors
Progress in Retinal and Eye Research, 2001Co-Authors: Nathan S HartAbstract:The spectral sensitivities of avian retinal photoreceptors are examined with respect to microspectrophotometric measurements of single cells, spectrophotometric measurements of extracted or in vitro regenerated Visual Pigments, and molecular genetic analyses of Visual Pigment opsin protein sequences. Bird species from diverse orders are compared in relation to their evolution, their habitats and the multiplicity of Visual tasks they must perform. Birds have five different types of Visual Pigment and seven different types of photo receptor-rods, double (uneven twin) cones and four types of single cone. The spectral locations of the wavelengths of maximum absorbance (lambda (max)) of the different Visual Pigments, and the spectral transmittance characteristics of the intraocular spectral filters (cone oil droplets) that also determine photoreceptor spectral sensitivity, vary according to both habitat and phylogenetic relatedness. The primary influence on avian retinal design appears to be the range of wavelengths available for vision, regardless of whether that range is determined by the spectral distribution of the natural illumination or the spectral transmittance of the ocular media (cornea, aqueous humour, lens, vitreous humour). Nevertheless, other variations in spectral sensitivity exist that reflect the variability and complexity of avian Visual ecology. (C) 2001 Elsevier Science Ltd. All rights reserved.
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Visual Pigments oil droplets ocular media and cone photoreceptor distribution in two species of passerine bird the blue tit parus caeruleus l and the blackbird turdus merula l
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2000Co-Authors: Nathan S Hart, J C Partridge, Innes C Cuthill, Andrew T D BennettAbstract:The spectral absorption characteristics of the retinal photoreceptors of the blue tit (Parus caeruleus) and blackbird (Turdus merula) were investigated using microspectrophotometry. The retinae of both species contained rods, double cones and four spectrally distinct types of single cone. Whilst the Visual Pigments and cone oil droplets in the other receptor types are very similar in both species, the wavelength of maximum sensitivity (λmax) of long-wavelength-sensitive single and double cone Visual Pigment occurs at a shorter wavelength (557 nm) in the blackbird than in the blue tit (563 nm). Oil droplets located in the long-wavelength-sensitivesingle cones of both species cut off wavelengths below 570–573 nm, theoretically shifting cone peak spectral sensitivity some 40 nm towards the long-wavelength end of the spectrum. This raises the possibility that the precise λmax of the long-wavelength-sensitive Visual Pigment is optimised for the Visual function of the double cones. The distribution of cone photoreceptors across the retina, determined using conventional light and fluorescence microscopy, also varies between the two species and may reflect differences in their Visual ecology.
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Visual Pigments cone oil droplets ocular media and predicted spectral sensitivity in the domestic turkey meleagris gallopavo
Vision Research, 1999Co-Authors: Nathan S Hart, J C Partridge, Innes C CuthillAbstract:A microspectrophotometric survey conducted on the retinal photoreceptors of the domestic turkey (Meleagris gallopavo) revealed the presence of five different types of vitamin A1-based Visual Pigment (rhodopsin) in seven different types of photoreceptor. A single class of rod contained a medium wavelength-sensitive Visual Pigment (wavelength of maximum absorbance, λmax, 504 nm). Four different types of single cone contained Visual Pigment maximally sensitive to wavelengths in either the long (LWS, λmax 564 nm), medium (MWS, λmax 505 nm), short (SWS, λmax 460 nm) or violet (VS, λmax 420 nm) spectral ranges. The LWS, MWS and SWS single cones contained Pigmented oil droplets with cut-off wavelengths (λcut) at 514, 490 and 437 nm, respectively. The VS single cone contained a transparent oil droplet which displayed no significant absorbance above 330 nm. A single class of double cone was also identified, both the principal and accessory members of which contained the LWS cone Visual Pigment. The principal member contained an oil droplet with a λcut at 436 nm. No oil droplet was observed in the accessory member. The use of a glycerol-based cell mountant, which reduced wavelength dependent measurement artefacts in the microspectrophotometric measurements, is described. Predictions of cone effective spectral sensitivity, incorporating measurements of the spectral transmission of the ocular media, suggest that turkeys have considerable sensitivity to wavelengths in the ultraviolet-A (UV-A, 315–400 nm) spectral range. This has implications for both the Visual ecology of wild birds and the welfare of intensively farmed individuals.
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Visual Pigments oil droplets and cone photoreceptor distribution in the european starling sturnus vulgaris
The Journal of Experimental Biology, 1998Co-Authors: Nathan S Hart, J C Partridge, Innes C CuthillAbstract:Microspectrophotometric measurements of retinal photoreceptors from the European starling (Sturnus vulgaris) revealed four classes of single cone, containing Visual Pigments with wavelengths of maximum absorbance ( max) at 563, 504, 449 and close to 362 nm. The two longer-wave-sensitive single cones contained brightly coloured oil droplets which cut off light below 572 and 514 nm, respectively. The 449 nm max Pigment was associated with a 'colourless' oil droplet with peak measured absorptance below 400 nm. The ultraviolet-sensitive Visual Pigment was paired with a transparent oil droplet which showed no significant absorption above 350 nm. A single class of double cone was identified, both members of which contained the longwave-sensitive ( max 563 nm) Visual Pigment. The principal member of the double cone contained an oil droplet with a topographically variable cut-off wavelength below 471 nm; the oil droplet found in the accessory member was only measured in the ventral retina and displayed three distinct peaks of absorption at approximately 430, 450 and 480 nm. Rod photoreceptors had a max at 503 nm. A new polynomial for fitting Visual Pigment templates to ultraviolet-sensitive Visual Pigment data is given. Topographic density measurements of the different cone classes were made using Nitroblue-tetrazolium chloride to label selectively bleached photoreceptors. The two classes of shortwave-sensitive single cone were more abundant in the dorsal retina, and longwave-sensitive single cones were notably less abundant in the dorso-temporal region of the retina, which subserves binocular vision.
Innes C Cuthill - One of the best experts on this subject based on the ideXlab platform.
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Visual Pigments oil droplets ocular media and cone photoreceptor distribution in two species of passerine bird the blue tit parus caeruleus l and the blackbird turdus merula l
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2000Co-Authors: Nathan S Hart, J C Partridge, Innes C Cuthill, Andrew T D BennettAbstract:The spectral absorption characteristics of the retinal photoreceptors of the blue tit (Parus caeruleus) and blackbird (Turdus merula) were investigated using microspectrophotometry. The retinae of both species contained rods, double cones and four spectrally distinct types of single cone. Whilst the Visual Pigments and cone oil droplets in the other receptor types are very similar in both species, the wavelength of maximum sensitivity (λmax) of long-wavelength-sensitive single and double cone Visual Pigment occurs at a shorter wavelength (557 nm) in the blackbird than in the blue tit (563 nm). Oil droplets located in the long-wavelength-sensitivesingle cones of both species cut off wavelengths below 570–573 nm, theoretically shifting cone peak spectral sensitivity some 40 nm towards the long-wavelength end of the spectrum. This raises the possibility that the precise λmax of the long-wavelength-sensitive Visual Pigment is optimised for the Visual function of the double cones. The distribution of cone photoreceptors across the retina, determined using conventional light and fluorescence microscopy, also varies between the two species and may reflect differences in their Visual ecology.
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Visual Pigments cone oil droplets ocular media and predicted spectral sensitivity in the domestic turkey meleagris gallopavo
Vision Research, 1999Co-Authors: Nathan S Hart, J C Partridge, Innes C CuthillAbstract:A microspectrophotometric survey conducted on the retinal photoreceptors of the domestic turkey (Meleagris gallopavo) revealed the presence of five different types of vitamin A1-based Visual Pigment (rhodopsin) in seven different types of photoreceptor. A single class of rod contained a medium wavelength-sensitive Visual Pigment (wavelength of maximum absorbance, λmax, 504 nm). Four different types of single cone contained Visual Pigment maximally sensitive to wavelengths in either the long (LWS, λmax 564 nm), medium (MWS, λmax 505 nm), short (SWS, λmax 460 nm) or violet (VS, λmax 420 nm) spectral ranges. The LWS, MWS and SWS single cones contained Pigmented oil droplets with cut-off wavelengths (λcut) at 514, 490 and 437 nm, respectively. The VS single cone contained a transparent oil droplet which displayed no significant absorbance above 330 nm. A single class of double cone was also identified, both the principal and accessory members of which contained the LWS cone Visual Pigment. The principal member contained an oil droplet with a λcut at 436 nm. No oil droplet was observed in the accessory member. The use of a glycerol-based cell mountant, which reduced wavelength dependent measurement artefacts in the microspectrophotometric measurements, is described. Predictions of cone effective spectral sensitivity, incorporating measurements of the spectral transmission of the ocular media, suggest that turkeys have considerable sensitivity to wavelengths in the ultraviolet-A (UV-A, 315–400 nm) spectral range. This has implications for both the Visual ecology of wild birds and the welfare of intensively farmed individuals.
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Visual Pigments oil droplets and cone photoreceptor distribution in the european starling sturnus vulgaris
The Journal of Experimental Biology, 1998Co-Authors: Nathan S Hart, J C Partridge, Innes C CuthillAbstract:Microspectrophotometric measurements of retinal photoreceptors from the European starling (Sturnus vulgaris) revealed four classes of single cone, containing Visual Pigments with wavelengths of maximum absorbance ( max) at 563, 504, 449 and close to 362 nm. The two longer-wave-sensitive single cones contained brightly coloured oil droplets which cut off light below 572 and 514 nm, respectively. The 449 nm max Pigment was associated with a 'colourless' oil droplet with peak measured absorptance below 400 nm. The ultraviolet-sensitive Visual Pigment was paired with a transparent oil droplet which showed no significant absorption above 350 nm. A single class of double cone was identified, both members of which contained the longwave-sensitive ( max 563 nm) Visual Pigment. The principal member of the double cone contained an oil droplet with a topographically variable cut-off wavelength below 471 nm; the oil droplet found in the accessory member was only measured in the ventral retina and displayed three distinct peaks of absorption at approximately 430, 450 and 480 nm. Rod photoreceptors had a max at 503 nm. A new polynomial for fitting Visual Pigment templates to ultraviolet-sensitive Visual Pigment data is given. Topographic density measurements of the different cone classes were made using Nitroblue-tetrazolium chloride to label selectively bleached photoreceptors. The two classes of shortwave-sensitive single cone were more abundant in the dorsal retina, and longwave-sensitive single cones were notably less abundant in the dorso-temporal region of the retina, which subserves binocular vision.
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Visual Pigments oil droplets and cone photoreceptor distribution in the european starling sturnus vulgaris
The Journal of Experimental Biology, 1998Co-Authors: Nathan S Hart, J C Partridge, Innes C CuthillAbstract:Microspectrophotometric measurements of retinal photoreceptors from the European starling (Sturnus vulgaris) revealed four classes of single cone, containing Visual Pigments with wavelengths of maximum absorbance ( max) at 563, 504, 449 and close to 362 nm. The two longer-wave-sensitive single cones contained brightly coloured oil droplets which cut off light below 572 and 514 nm, respectively. The 449 nm max Pigment was associated with a 9colourless9 oil droplet with peak measured absorptance below 400 nm. The ultraviolet-sensitive Visual Pigment was paired with a transparent oil droplet which showed no significant absorption above 350 nm. A single class of double cone was identified, both members of which contained the longwave-sensitive ( max 563 nm) Visual Pigment. The principal member of the double cone contained an oil droplet with a topographically variable cut-off wavelength below 471 nm; the oil droplet found in the accessory member was only measured in the ventral retina and displayed three distinct peaks of absorption at approximately 430, 450 and 480 nm. Rod photoreceptors had a max at 503 nm. A new polynomial for fitting Visual Pigment templates to ultraviolet-sensitive Visual Pigment data is given. Topographic density measurements of the different cone classes were made using Nitroblue-tetrazolium chloride to label selectively bleached photoreceptors. The two classes of shortwave-sensitive single cone were more abundant in the dorsal retina, and longwave-sensitive single cones were notably less abundant in the dorso-temporal region of the retina, which subserves binocular vision.
Belinda S. W. Chang - One of the best experts on this subject based on the ideXlab platform.
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to see or not to see molecular evolution of the rhodopsin Visual Pigment in neotropical electric fishes
Proceedings of The Royal Society B: Biological Sciences, 2019Co-Authors: Alexander Van Nynatten, Belinda S. W. Chang, Francesco H Janzen, Kristen Brochu, Javier A Maldonadoocampo, William G R Crampton, Nathan R LovejoyAbstract:Functional variation in rhodopsin, the dim-light-specialized Visual Pigment, frequently occurs in species inhabiting light-limited environments. Variation in Visual function can arise through two processes: relaxation of selection or adaptive evolution improving photon detection in a given environment. Here, we investigate the molecular evolution of rhodopsin in Gymnotiformes, an order of mostly nocturnal South American fishes that evolved sophisticated electrosensory capabilities. Our initial sequencing revealed a mutation associated with Visual disease in humans. As these fishes are thought to have poor vision, this would be consistent with a possible sensory trade-off between the Visual system and a novel electrosensory system. To investigate this, we surveyed rhodopsin from 147 gymnotiform species, spanning the order, and analysed patterns of molecular evolution. In contrast with our expectation, we detected strong selective constraint in gymnotiform rhodopsin, with rates of non-synonymous to synonymous substitutions lower in gymnotiforms than in other vertebrate lineages. In addition, we found evidence for positive selection on the branch leading to gymnotiforms and on a branch leading to a clade of deep-channel specialized gymnotiform species. We also found evidence that deleterious effects of a human disease-associated substitution are likely to be masked by epistatic substitutions at nearby sites. Our results suggest that rhodopsin remains an important component of the gymnotiform sensory system alongside electrolocation, and that photosensitivity of rhodopsin is well adapted for vision in dim-light environments.
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functional shifts in bat dim light Visual Pigment are associated with differing echolocation abilities and reveal molecular adaptation to photic limited environments
Molecular Biology and Evolution, 2018Co-Authors: Eduardo De A Gutierrez, James M Morrow, Gianni M Castiglione, Ryan K Schott, Livia O Loureiro, Burton K Lim, Belinda S. W. ChangAbstract:Bats are excellent models for studying the molecular basis of sensory adaptation. In Chiroptera, a sensory trade-off has been proposed between the Visual and auditory systems, though the extent of this association has yet to be fully examined. To investigate whether variation in Visual performance is associated with echolocation, we experimentally assayed the dim-light Visual Pigment rhodopsin from bat species with differing echolocation abilities. While spectral tuning properties were similar among bats, we found that the rate of decay of their light-activated state was significantly slower in a nonecholocating bat relative to species that use distinct echolocation strategies, consistent with a sensory trade-off hypothesis. We also found that these rates of decay were remarkably slower compared with those of other mammals, likely indicating an adaptation to dim light. To examine whether functional changes in rhodopsin are associated with shifts in selection intensity upon bat Rh1 sequences, we implemented selection analyses using codon-based likelihood clade models. While no shifts in selection were identified in response to diverse echolocation abilities of bats, we detected a significant increase in the intensity of evolutionary constraint accompanying the diversification of Chiroptera. Taken together, this suggests that substitutions that modulate the stability of the light-activated rhodopsin state were likely maintained through intensified constraint after bats diversified, being finely tuned in response to novel sensory specializations. Our study demonstrates the power of combining experimental and computational approaches for investigating functional mechanisms underlying the evolution of complex sensory adaptations.
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insights into Visual Pigment adaptation and diversity from model ecological and evolutionary systems
Current Opinion in Genetics & Development, 2017Co-Authors: Frances E Hauser, Belinda S. W. ChangAbstract:Sensory systems provide valuable insight into the evolution of molecular mechanisms underlying organismal anatomy, physiology, and behaviour. Visual Pigments, which mediate the first step in Visual transduction, offer a unique window into the relationship between molecular variation and Visual performance, and enhance our understanding of how ecology, life history, and physiology may shape genetic variation across a variety of organisms. Here we review recent work investigating vertebrate Visual Pigments from a number of perspectives. Opsin gene duplication, loss, differential expression, structural variation, and the physiological context in which they operate, have profoundly shaped the Visual capabilities of vertebrates adapting to novel environments. We note the importance of conceptual frameworks in investigating Visual Pigment diversity in vertebrates, highlighting key examples including evolutionary transitions between different photic environments, major shifts in life history evolution and ecology, evolutionary innovations in Visual system anatomy and physiology, as well as shifts in Visually mediated behaviours and behavioural ecology. We emphasize the utility of studying Visual Pigment evolution in the context of these different perspectives, and demonstrate how the integrative approaches discussed in this review contribute to a better understanding of the underlying molecular processes mediating adaptation in sensory systems, and the contexts in which they occur.
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out of the blue adaptive Visual Pigment evolution accompanies amazon invasion
Biology Letters, 2015Co-Authors: Alexander Van Nynatten, Belinda S. W. Chang, Devin D Bloom, Nathan R LovejoyAbstract:Incursions of marine water into South America during the Miocene prompted colonization of freshwater habitats by ancestrally marine species and present a unique opportunity to study the molecular evolution of adaptations to varying environments. Freshwater and marine environments are distinct in both spectra and average intensities of available light. Here, we investigate the molecular evolution of rhodopsin, the photosensitive Pigment in the eye that activates in response to light, in a clade of South American freshwater anchovies derived from a marine ancestral lineage. Using likelihood-based comparative sequence analyses, we found evidence for positive selection in the rhodopsin of freshwater anchovy lineages at sites known to be important for aspects of rhodopsin function such as spectral tuning. No evidence was found for positive selection in marine lineages, nor in three other genes not involved in vision. Our results suggest that an increased rate of rhodopsin evolution was driven by diversification into freshwater habitats, thereby constituting a rare example of molecular evolution mirroring large-scale palaeogeographic events.
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sws2 Visual Pigment evolution as a test of historically contingent patterns of plumage color evolution in warblers
Evolution, 2015Co-Authors: Natasha I Bloch, Belinda S. W. Chang, James M Morrow, Trevor D PriceAbstract:Distantly related clades that occupy similar environments may differ due to the lasting imprint of their ancestors – historical contingency. The New World warblers (Parulidae) and Old World warblers (Phylloscopidae) are ecologically similar clades that differ strikingly in plumage coloration. We studied genetic and functional evolution of the short-wavelength sensitive Visual Pigments (SWS2 and SWS1) to ask if altered color perception could contribute to the plumage color differences between clades. We show SWS2 is short-wavelength shifted in birds that occupy open environments, such as finches, compared to those in closed environments, including warblers. Phylogenetic reconstructions indicate New World warblers were derived from a finch-like form that colonized from the Old World 15-20Ma. During this process the SWS2 gene accumulated 6 substitutions in branches leading to New World warblers, inviting the hypothesis that passage through a finch-like ancestor resulted in SWS2 evolution. In fact, we show spectral tuning remained similar across warblers as well as the finch ancestor. Results reject the hypothesis of historical contingency based on opsin spectral tuning, but point to evolution of other aspects of Visual Pigment function. Using the approach outlined here, historical contingency becomes a generally testable theory in systems where genotype and phenotype can be connected.
J C Partridge - One of the best experts on this subject based on the ideXlab platform.
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Visual Pigments oil droplets ocular media and cone photoreceptor distribution in two species of passerine bird the blue tit parus caeruleus l and the blackbird turdus merula l
Journal of Comparative Physiology A-neuroethology Sensory Neural and Behavioral Physiology, 2000Co-Authors: Nathan S Hart, J C Partridge, Innes C Cuthill, Andrew T D BennettAbstract:The spectral absorption characteristics of the retinal photoreceptors of the blue tit (Parus caeruleus) and blackbird (Turdus merula) were investigated using microspectrophotometry. The retinae of both species contained rods, double cones and four spectrally distinct types of single cone. Whilst the Visual Pigments and cone oil droplets in the other receptor types are very similar in both species, the wavelength of maximum sensitivity (λmax) of long-wavelength-sensitive single and double cone Visual Pigment occurs at a shorter wavelength (557 nm) in the blackbird than in the blue tit (563 nm). Oil droplets located in the long-wavelength-sensitivesingle cones of both species cut off wavelengths below 570–573 nm, theoretically shifting cone peak spectral sensitivity some 40 nm towards the long-wavelength end of the spectrum. This raises the possibility that the precise λmax of the long-wavelength-sensitive Visual Pigment is optimised for the Visual function of the double cones. The distribution of cone photoreceptors across the retina, determined using conventional light and fluorescence microscopy, also varies between the two species and may reflect differences in their Visual ecology.
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Visual Pigments cone oil droplets ocular media and predicted spectral sensitivity in the domestic turkey meleagris gallopavo
Vision Research, 1999Co-Authors: Nathan S Hart, J C Partridge, Innes C CuthillAbstract:A microspectrophotometric survey conducted on the retinal photoreceptors of the domestic turkey (Meleagris gallopavo) revealed the presence of five different types of vitamin A1-based Visual Pigment (rhodopsin) in seven different types of photoreceptor. A single class of rod contained a medium wavelength-sensitive Visual Pigment (wavelength of maximum absorbance, λmax, 504 nm). Four different types of single cone contained Visual Pigment maximally sensitive to wavelengths in either the long (LWS, λmax 564 nm), medium (MWS, λmax 505 nm), short (SWS, λmax 460 nm) or violet (VS, λmax 420 nm) spectral ranges. The LWS, MWS and SWS single cones contained Pigmented oil droplets with cut-off wavelengths (λcut) at 514, 490 and 437 nm, respectively. The VS single cone contained a transparent oil droplet which displayed no significant absorbance above 330 nm. A single class of double cone was also identified, both the principal and accessory members of which contained the LWS cone Visual Pigment. The principal member contained an oil droplet with a λcut at 436 nm. No oil droplet was observed in the accessory member. The use of a glycerol-based cell mountant, which reduced wavelength dependent measurement artefacts in the microspectrophotometric measurements, is described. Predictions of cone effective spectral sensitivity, incorporating measurements of the spectral transmission of the ocular media, suggest that turkeys have considerable sensitivity to wavelengths in the ultraviolet-A (UV-A, 315–400 nm) spectral range. This has implications for both the Visual ecology of wild birds and the welfare of intensively farmed individuals.
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Visual Pigments oil droplets and cone photoreceptor distribution in the european starling sturnus vulgaris
The Journal of Experimental Biology, 1998Co-Authors: Nathan S Hart, J C Partridge, Innes C CuthillAbstract:Microspectrophotometric measurements of retinal photoreceptors from the European starling (Sturnus vulgaris) revealed four classes of single cone, containing Visual Pigments with wavelengths of maximum absorbance ( max) at 563, 504, 449 and close to 362 nm. The two longer-wave-sensitive single cones contained brightly coloured oil droplets which cut off light below 572 and 514 nm, respectively. The 449 nm max Pigment was associated with a 'colourless' oil droplet with peak measured absorptance below 400 nm. The ultraviolet-sensitive Visual Pigment was paired with a transparent oil droplet which showed no significant absorption above 350 nm. A single class of double cone was identified, both members of which contained the longwave-sensitive ( max 563 nm) Visual Pigment. The principal member of the double cone contained an oil droplet with a topographically variable cut-off wavelength below 471 nm; the oil droplet found in the accessory member was only measured in the ventral retina and displayed three distinct peaks of absorption at approximately 430, 450 and 480 nm. Rod photoreceptors had a max at 503 nm. A new polynomial for fitting Visual Pigment templates to ultraviolet-sensitive Visual Pigment data is given. Topographic density measurements of the different cone classes were made using Nitroblue-tetrazolium chloride to label selectively bleached photoreceptors. The two classes of shortwave-sensitive single cone were more abundant in the dorsal retina, and longwave-sensitive single cones were notably less abundant in the dorso-temporal region of the retina, which subserves binocular vision.
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Visual Pigments oil droplets and cone photoreceptor distribution in the european starling sturnus vulgaris
The Journal of Experimental Biology, 1998Co-Authors: Nathan S Hart, J C Partridge, Innes C CuthillAbstract:Microspectrophotometric measurements of retinal photoreceptors from the European starling (Sturnus vulgaris) revealed four classes of single cone, containing Visual Pigments with wavelengths of maximum absorbance ( max) at 563, 504, 449 and close to 362 nm. The two longer-wave-sensitive single cones contained brightly coloured oil droplets which cut off light below 572 and 514 nm, respectively. The 449 nm max Pigment was associated with a 9colourless9 oil droplet with peak measured absorptance below 400 nm. The ultraviolet-sensitive Visual Pigment was paired with a transparent oil droplet which showed no significant absorption above 350 nm. A single class of double cone was identified, both members of which contained the longwave-sensitive ( max 563 nm) Visual Pigment. The principal member of the double cone contained an oil droplet with a topographically variable cut-off wavelength below 471 nm; the oil droplet found in the accessory member was only measured in the ventral retina and displayed three distinct peaks of absorption at approximately 430, 450 and 480 nm. Rod photoreceptors had a max at 503 nm. A new polynomial for fitting Visual Pigment templates to ultraviolet-sensitive Visual Pigment data is given. Topographic density measurements of the different cone classes were made using Nitroblue-tetrazolium chloride to label selectively bleached photoreceptors. The two classes of shortwave-sensitive single cone were more abundant in the dorsal retina, and longwave-sensitive single cones were notably less abundant in the dorso-temporal region of the retina, which subserves binocular vision.
Karen L. Carleton - One of the best experts on this subject based on the ideXlab platform.
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spectral tuning by opsin coexpression in retinal regions that view different parts of the Visual field
Proceedings of The Royal Society B: Biological Sciences, 2014Co-Authors: Brian E Dalton, Ellis R. Loew, Thomas W. Cronin, Karen L. CarletonAbstract:Vision frequently mediates critical behaviours, and photoreceptors must respond to the light available to accomplish these tasks. Most photoreceptors are thought to contain a single Visual Pigment, an opsin protein bound to a chromophore, which together determine spectral sensitivity. Mechanisms of spectral tuning include altering the opsin, changing the chromophore and incorporating pre-receptor filtering. A few exceptions to the use of a single Visual Pigment have been documented in which a single mature photoreceptor coexpresses opsins that form spectrally distinct Visual Pigments, and in these exceptions the functional significance of coexpression is unclear. Here we document for the first time photoreceptors coexpressing spectrally distinct opsin genes in a manner that tunes sensitivity to the light environment. Photoreceptors of the cichlid fish, Metriaclima zebra , mix different pairs of opsins in retinal regions that view distinct backgrounds. The mixing of Visual Pigments increases absorbance of the corresponding background, potentially aiding the detection of dark objects. Thus, opsin coexpression may be a novel mechanism of spectral tuning that could be useful for detecting prey, predators and mates. However, our calculations show that coexpression of some opsins can hinder colour discrimination, creating a trade-off between Visual functions.
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Visual photoPigment evolution in speciation
2014Co-Authors: Karen L. CarletonAbstract:Visual Pigment sensitivities are known to vary across organisms and habitats. The sensory drive theory was formulated over 20 years ago to help explain how such sensory variation could contribute to divergent selection and speciation. Since then, there have been only a few examples that support the idea that Visual Pigment evolution contributes to speciation. Here, I discuss what is required to demonstrate that evolution of Visual Pigments (and Visual sensitivities) play a role speciation. I then identify systems where Visual Pigments are unlikely to have a role, where they might play a role, and where they likely have driven speciation. This review concludes that more examples are needed to identify instances where Visual Pigment evolution contributes to speciation and to determine how frequently sensory drive is at work.
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the eyes have it regulatory and structural changes both underlie cichlid Visual Pigment diversity
PLOS Biology, 2009Co-Authors: Christopher M Hofmann, Thomas W. Cronin, Kelly E Oquin, Justin N Marshall, Ole Seehausen, Karen L. CarletonAbstract:A major goal of evolutionary biology is to unravel the molecular genetic mechanisms that underlie functional diversification and adaptation. We investigated how changes in gene regulation and coding sequence contribute to sensory diversification in two replicate radiations of cichlid fishes. In the clear waters of Lake Malawi, differential opsin expression generates diverse Visual systems, with sensitivities extending from the ultraviolet to the red regions of the spectrum. These sensitivities fall into three distinct clusters and are correlated with foraging habits. In the turbid waters of Lake Victoria, Visual sensitivity is constrained to longer wavelengths, and opsin expression is correlated with ambient light. In addition to regulatory changes, we found that the opsins coding for the shortest- and longest-wavelength Visual Pigments have elevated numbers of potentially functional substitutions. Thus, we present a model of sensory evolution in which both molecular genetic mechanisms work in concert. Changes in gene expression generate large shifts in Visual Pigment sensitivity across the collective opsin spectral range, but changes in coding sequence appear to fine-tune Visual Pigment sensitivity at the short- and long-wavelength ends of this range, where differential opsin expression can no longer extend Visual Pigment sensitivity.
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Cone Opsin Genes of African Cichlid Fishes: Tuning Spectral Sensitivity by Differential Gene Expression
Molecular Biology and Evolution, 2001Co-Authors: Karen L. Carleton, Thomas KocherAbstract:Spectral tuning of Visual Pigments is typically accomplished through changes in opsin amino acid sequence. Within a given opsin class, changes at a few key sites control wavelength specificity. To investigate known differences in the Visual Pigment spectral sensitivity of the Lake Malawi cichlids, Metriaclima zebra (368, 488, and 533 nm) and Dimidiochromis compressiceps (447, 536, and 569 nm), we sequenced cone opsin genes from these species as well as Labeotropheus fuelleborni and Oreochromis niloticus. These cichlids have five distinct classes of cone opsin genes, including two unique SWS-2 genes. Comparisons of the inferred amino acid sequences from the five cone opsin genes of M. zebra, D. compressiceps, and L. fuelleborni show the sequences to be nearly identical. Therefore, evolution of key opsin sites cannot explain the differences in Visual Pigment sensitivities. Real-time PCR demonstrates that different cichlid species express different subsets of the available cone opsin genes. Metriaclima zebra and L. fuelleborni express a complement of genes which give them UV-shifted Visual Pigments, while D. compressiceps expresses a different set to produce a red-shifted Visual system. Thus, variations in cichlid spectral sensitivity have arisen through evolution of gene regulation, rather than through changes in opsin amino acid sequence.
