Visual pigments in a palaeognath bird, the emu<i>Dromaius novaehollandiae</i>: implications for spectral sensitivity and the origin of ultraviolet vision

Hart, Nathan S.; Mountford, Jessica Kate; Collin, Shaun P.; Hunt, David M.

doi:10.1098/rspb.2016.1063

Cited by 17 publications

(11 citation statements)

References 68 publications

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“…It is possible that the common reptilian ancestor of birds had a violet SWS1, but that some avian groups reevolved UV sensitivity, often through the alternative tuning site at position 90 (Hunt et al, 2004;Ödeen and Håstad, 2013). By contrast, the recent discovery of a UVS cone type in the emu, a paleognath bird basal in avian evolution (Hart et al, 2016), is consistent with the presence of UVS visual pigments in the earliest birds and thus their ancestors. It should be noted that, with the exception of teleosts, vertebrates typically only possess one copy of SWS1, making the tuning of this opsin sequence critical in spectrally mediated visual tasks.…”

Section: Spectral Tuning Of Uv Opsinsmentioning

confidence: 89%

Photoreception and vision in the ultraviolet

Cronin

Bok

2016

Journal of Experimental Biology

154

128

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Ultraviolet (UV) light occupies the spectral range of wavelengths slightly shorter than those visible to humans. Because of its shorter wavelength, it is more energetic (and potentially more photodamaging) than 'visible light', and it is scattered more efficiently in air and water. Until 1990, only a few animals were recognized as being sensitive to UV light, but we now know that a great diversity, possibly even the majority, of animal species can visually detect and respond to it. Here, we discuss the history of research on biological UV photosensitivity and review current major research trends in this field. Some animals use their UV photoreceptors to control simple, innate behaviors, but most incorporate their UV receptors into their general sense of vision. They not only detect UV light but recognize it as a separate color in light fields, on natural objects or living organisms, or in signals displayed by conspecifics. UV visual pigments are based on opsins, the same family of proteins that are used to detect light in conventional photoreceptors. Despite some interesting exceptions, most animal species have a single photoreceptor class devoted to the UV. The roles of UV in vision are manifold, from guiding navigation and orientation behavior, to detecting food and potential predators, to supporting high-level tasks such as mate assessment and intraspecific communication. Our current understanding of UV vision is restricted almost entirely to two phyla: arthropods and chordates (specifically, vertebrates), so there is much comparative work to be done.

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Section: Spectral Tuning Of Uv Opsinsmentioning

confidence: 89%

Photoreception and vision in the ultraviolet

Cronin

Bok

2016

Journal of Experimental Biology

154

128

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“…Given that the common ostrich – the phylogenetically most basal bird in our sample – has large eyes and an intermediate λ T0.5 , an unpigmented lens is the most likely ancestral state. The ancestral state of the SWS1 opsin seems to be UV sensitivity ( Hart et al, 2016 ), and violet and UV sensitivity have evolved repeatedly ( Ödeen and Håstad, 2013 ). From this hypothetical ancestral state – intermediate OMT with an unpigmented lens and a UVS visual pigment – two directions have been taken by different groups of birds.…”

Section: Discussionmentioning

confidence: 99%

Lens and cornea limit UV vision of birds – a phylogenetic perspective

Olsson

Lind

Mitkus

et al. 2021

Journal of Experimental Biology

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Most vertebrates have UV-sensitive vision, but the UV-sensitivity of their eyes is limited by the transmittance of the ocular media, and the specific contribution of the different media (cornea, lens) has remained unclear. Here we describe the transmittance of all ocular media (OMT), as well as that of lenses and corneas of birds. For 66 species belonging to 18 orders, the wavelength at which 50% of light is transmitted through the ocular media to the retina (λT0.5) ranges from 310 to 398 nm. Low λT0.5 corresponds to more UV-light transmitted. Corneal λT0.5 varies only between 300 and 345 nm, whereas lens λT0.5 values are more variable (between 315 and 400 nm) and tend to be the limiting factor, determining OMT in the majority of species. OMT λT0.5 is positively correlated with eye size, but λT0.5 of corneas and lenses are not correlated with their thickness when controlled for phylogeny. Corneal and lens transmittances do not differ between birds with UV- and violet-sensitive SWS1 opsin when controlling for eye size and phylogeny. Phylogenetic relatedness is a strong predictor of OMT, and ancestral state reconstructions suggest that from ancestral intermediate OMT, highly UV-transparent ocular media (low λT0.5) evolved at least five times in our sample of birds. Some birds have evolved in the opposite direction towards a more UV-opaque lens, possibly due to pigmentation, likely to mitigate UV-damage or reduce chromatic aberration.

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“…Complementary DNA (cDNA) was subsequently generated using 2 g of total RNA and the miScript II Reverse Transcription (RT) Kit (Qiagen, Australia), according to the manufacturer's instructions. The LWS, SWS1, SWS2, RH2 and RH1 genes were PCR amplified according to Davies et al (2009) from cDNA using degenerate primers listed in Supplementary Table S1 and as for the amplification of the rod (RH1) gene (Davies et al, 2009;Hart et al, 2016;Knott et al, 2013).…”

Section: Isolation and Sequencing Of Opsin Mrnamentioning

confidence: 99%

Enhanced short-wavelength sensitivity in the blue-tongued skink, Tiliqua rugosa

Nagloo

Mountford

Gundry

et al. 2022

Preprint

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The complex visually mediated behaviors of diurnal lizards are enabled by a retina typically containing five types of opsins with the potential for tetrachromatic color vision. Despite lizards using a wide range of color signals, the limited variation in photoreceptor spectral sensitivities across lizards suggests only weak selection for species–specific, spectral tuning of photoreceptors. Some species, however, have enhanced short wavelength sensitivity, which likely helps with the detection of signals rich in ultraviolet and short wavelengths. In this study, we examined the visual system of Tiliqua rugosa,which has a UV–blue tongue, to determine the spectral sensitivity of the eye and to gain insight into this species' visual ecology. Electroretinograms coupled with spectral stimulation showed peak sensitivity at 560 nm with high similarity to other lizards at wavelengths greater than 530 nm. However, at shorter wavelengths, sensitivity is enhanced leading to a spectral sensitivity curve that is 28 nm broader (full width at half height) than other lizards studied so far. The width of the curve is partially explained by a population of photoreceptors that respond more strongly to low temporal frequencies with possible peaks in sensitivity between 460 and 470 nm suggesting that they are SWS2 photoreceptors. The lack of a peak in sensitivity at 360 nm at low temporal frequencies and under a monochromatic light that suppresses the response of LWS photoreceptors, suggests that the SWS1 photoreceptors are red–shifted. In addition, the yellow and green oil droplets that are common in other diurnal lizards appear to be missing and instead, only transparent and pale–yellow oil droplets are present. LWS photoreceptors are likely paired with pale–yellow oil droplets to produce LWS photoreceptors with wider spectral sensitivity curves than in other lizards. Opsin sequencing reveals SWS1, SWS2, RH1, RH2 and LWS opsin genes that are very similar to the visual opsins detected in the green anole, Anolis carolinensis, suggesting there is little change in the spectral sensitivity of photoreceptors compared to other diurnal lizards. Since we only obtained a partial sequence of the SWS1 opsin, we were unable to determine whether amino acid substitution at tuning sites could have played a role in red–shifting the SWS1 photoreceptor spectral sensitivity. Photoreceptor densities are typically higher in central and ventral retinal regions than in the dorsal retina suggesting that higher spatial sampling is necessary at eye level and above the animal than on the ground. However, the SWS1 photoreceptors do not follow this pattern potentially due to their low abundance making them less relevant to high acuity visual tasks. Our findings demonstrate that there are possibly multiple mechanisms acting synergistically in the visual system of T. rugosa to enhance short wavelength sensitivity between 360 and 530 nm. While it is tempting to suggest that this is an adaptation to facilitate the detection of the blue tongues of conspecifics, additional experiments are necessary to determine its ecological relevance.

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Visual pigments in a palaeognath bird, the emuDromaius novaehollandiae: implications for spectral sensitivity and the origin of ultraviolet vision

Cited by 17 publications

References 68 publications

Photoreception and vision in the ultraviolet

Photoreception and vision in the ultraviolet

Lens and cornea limit UV vision of birds – a phylogenetic perspective

Enhanced short-wavelength sensitivity in the blue-tongued skink, Tiliqua rugosa

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