Why do green rods of frog and toad retinas look green?

Govardovskii, V. I.; Reuter, Tom

doi:10.1007/s00359-014-0925-z

Cited by 9 publications

(10 citation statements)

References 31 publications

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“…Thus, the decrease of the thermal isomerization rates of anuran blue-sensitive cone pigments in green rods enables them to function in tandem with green-sensitive red (normal) rods for scotopic vision, which could provide a molecular basis for color discrimination under the dark conditions. This theory is consistent with behavioral evidence that indicates that frogs can distinguish the colors blue and gray at low illumination levels, probably using green rods, in addition to color vision in photopic condition (35)(36)(37). Scotopic color vision may be advantageous for nocturnality that is observed in many anuran species (such as X. tropicalis and the American bullfrog).…”

Section: Mechanistic Implication Of the Low Thermal Isomerization Ratessupporting

confidence: 72%

Adaptation of cone pigments found in green rods for scotopic vision through a single amino acid mutation

Kojima

Matsutani

Yamashita

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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Most vertebrate retinas contain a single type of rod for scotopic vision and multiple types of cones for photopic and color vision. The retinas of certain amphibian species uniquely contain two types of rods: red rods, which express rhodopsin, and green rods, which express a blue-sensitive cone pigment (M1/SWS2 group). Spontaneous activation of rhodopsin induced by thermal isomerization of the retinal chromophore has been suggested to contribute to the rod's background noise, which limits the visual threshold for scotopic vision. Therefore, rhodopsin must exhibit low thermal isomerization rate compared with cone visual pigments to adapt to scotopic condition. In this study, we determined whether amphibian blue-sensitive cone pigments in green rods exhibit low thermal isomerization rates to act as rhodopsin-like pigments for scotopic vision. Anura blue-sensitive cone pigments exhibit low thermal isomerization rates similar to rhodopsin, whereas Urodela pigments exhibit high rates like other vertebrate cone pigments present in cones. Furthermore, by mutational analysis, we identified a key amino acid residue, Thr47, that is responsible for the low thermal isomerization rates of Anura blue-sensitive cone pigments. These results strongly suggest that, through this mutation, anurans acquired special blue-sensitive cone pigments in their green rods, which could form the molecular basis for scotopic color vision with normal red rods containing green-sensitive rhodopsin.photoreceptor cell | visual pigment | amphibian | molecular evolution | color discrimination

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Section: Mechanistic Implication Of the Low Thermal Isomerization Ratessupporting

confidence: 72%

Adaptation of cone pigments found in green rods for scotopic vision through a single amino acid mutation

Kojima

Matsutani

Yamashita

et al. 2017

Proc. Natl. Acad. Sci. U.S.A.

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“…Pupil shape and its contractility are of major importance to deal with different light intensities and to establish a suitable compromise between high acuity and sensitivity [73,74]. However, pupil shape diversity is only one aspect of the eye that is relevant from the perspective of the evolution of visual perception, others being for example eye size [30,75], cornea and lens transmittance [27,28], lens optics [32,76], photoreceptor composition and size [25,26], oil droplets and visual pigments [77][78][79][80], and neural pathways [22,81].…”

Section: (D) Pupil Shape Diversity and Visual Ecologymentioning

confidence: 99%

A closer look at pupil diversity and evolution in frogs and toads

et al. 2021

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The eyes of frogs and toads (Anura) are among their most fascinating features. Although several pupil shapes have been described, the diversity, evolution, and functional role of the pupil in anurans have received little attention. Studying photographs of more than 3200 species, we surveyed pupil diversity, described their morphological variation, tested correlation with adult habits and diel activity, and discuss major evolutionary patterns considering iris anatomy and visual ecology. Our results indicate that the pupil in anurans is a highly plastic structure, with seven main pupil shapes that evolved at least 116 times during the history of the group. We found no significant correlation between pupil shape, adult habits, and diel activity, with the exception of the circular pupil and aquatic habits. The vertical pupil arose at least in the most-recent common ancestor of Anura + Caudata, and this morphology is present in most early-diverging anuran clades. Subsequently, a horizontal pupil, a very uncommon shape in vertebrates, evolved in most neobatrachian frogs. This shape evolved into most other known pupil shapes, but it persisted in a large number of species with diverse life histories, habits, and diel activity patterns, demonstrating a remarkable functional and ecological versatility.

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“…This remarkable sensitivity of colour discrimination lies near the physical limits set by the quantum character of light, as can be seen from the following estimations of signal-to-noise ratios (SNR) in our experimental conditions. The retinal image of the window covers about 30 000 GS rods and 3000 BS rods [ 47 ]. Over this area, the light intensity 0.001 R* rod −1 s −1 (where green and blue are already distinguished) produces a total of around 30 R* s −1 in GS rods and 4 R* s −1 in BS rods.…”

Section: Phototaxis Experimentsmentioning

confidence: 99%

The dual rod system of amphibians supports colour discrimination at the absolute visual threshold

Yovanovich

Koskela

Nevala

et al. 2017

Phil. Trans. R. Soc. B

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The presence of two spectrally different kinds of rod photoreceptors in amphibians has been hypothesized to enable purely rod-based colour vision at very low light levels. The hypothesis has never been properly tested, so we performed three behavioural experiments at different light intensities with toads (Bufo) and frogs (Rana) to determine the thresholds for colour discrimination. The thresholds of toads were different in mate choice and prey-catching tasks, suggesting that the differential sensitivities of different spectral cone types as well as task-specific factors set limits for the use of colour in these behavioural contexts. In neither task was there any indication of rod-based colour discrimination. By contrast, frogs performing phototactic jumping were able to distinguish blue from green light down to the absolute visual threshold, where vision relies only on rod signals. The remarkable sensitivity of this mechanism comparing signals from the two spectrally different rod types approaches theoretical limits set by photon fluctuations and intrinsic noise. Together, the results indicate that different pathways are involved in processing colour cues depending on the ecological relevance of this information for each task.This article is part of the themed issue ‘Vision in dim light’.

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Why do green rods of frog and toad retinas look green?

Cited by 9 publications

References 31 publications

Adaptation of cone pigments found in green rods for scotopic vision through a single amino acid mutation

Adaptation of cone pigments found in green rods for scotopic vision through a single amino acid mutation

A closer look at pupil diversity and evolution in frogs and toads

The dual rod system of amphibians supports colour discrimination at the absolute visual threshold

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