The gecko retina

Tansley, Katharine

doi:10.1016/0042-6989(64)90029-x

Cited by 39 publications

(27 citation statements)

References 13 publications

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“…A similar situation exists in the pure rod retinas of nocturnal Tokay geckos (Crescitelli et al, 1977), where three of the cone pigment classes, SWS1, Rh2, and LWS, have been retained (Kojima et al, 1992;Yokoyama and Blow, 2001). In these geckos, the middle-wavelength-sensitive photoreceptors which are described as rod-like on the basis of morphology and sensitivity to light (Pedier and Tilly, 1964;Tansley, 1964;Kleinschmidt and Dowling, 1975;Rispoli et al, 1993) express a "cone" Rh2 gene (Yokoyama and Blow, 2001), consistent with Walls' transmutation theory (Walls, 1934(Walls, , 1942. In contrast, P. regius and X. unicolor have retained the Rh1 gene in their middle-wavelength-sensitive rod photoreceptors.…”

Section: Discussionmentioning

confidence: 92%

“…In this theory, Walls suggested that the duplex retinas of early terrestrial tetrapods lost all rods in response to a complete diurnal lifestyle with a sole dependency on sunlight. With the rise of birds and mammals and the ensuing complex prey-predator relationships, many reptiles became "secondarily" nocturnal and their cones "transmutated" into photoreceptors with rod-like characteristics of a lower activation threshold and an increased sensitivity to light (Pedier and Tilly, 1964;Tansley, 1964;Kleinschmidt and Dowling, 1975;Rispoli et al, 1993).…”

Section: Introductionmentioning

confidence: 99%

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Shedding Light on Serpent Sight: The Visual Pigments of Henophidian Snakes

Davies¹,

Cowing²,

Bowmaker³

et al. 2009

Journal of Neuroscience

112

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The biologist Gordon Walls proposed his "transmutation" theory through the 1930s and the 1940s to explain cone-like morphology of rods (and vice versa) in the duplex retinas of modern-day reptiles, with snakes regarded as the epitome of his hypothesis. Despite Walls' interest, the visual system of reptiles, and in particular snakes, has been widely neglected in favor of studies of fishes and mammals. By analyzing the visual pigments of two henophidian snakes, Xenopeltis unicolor and Python regius, we show that both species express two cone opsins, an ultraviolet-sensitive short-wavelength-sensitive 1 (SWS1) ( max ϭ 361 nm) pigment and a long-wavelength-sensitive (LWS) ( max ϭ 550 nm) pigment, providing the potential for dichromatic color vision. They also possess rod photoreceptors which express the usual rod opsin (Rh1) pigment with a max at 497 nm. This is the first molecular study of the visual pigments expressed in the photoreceptors of any snake species. The presence of a duplex retina and the characterization of LWS, SWS1, and Rh1 visual pigments in henophidian snakes implies that "lower" snakes do not provide support for Walls' transmutation theory, unlike some "higher" (caenophidian) snakes and other reptiles, such as geckos. More data from other snake lineages will be required to test this hypothesis further.

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Section: Discussionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Shedding Light on Serpent Sight: The Visual Pigments of Henophidian Snakes

Davies¹,

Cowing²,

Bowmaker³

et al. 2009

Journal of Neuroscience

112

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“…Evidence of cone-to-rod transmutation in nocturnal geckos has been extensively demonstrated using both cellular and molecular techniques (Crescitelli, 1956;Dodt and Walther, 1958;Kojima et al, 1992;McDevitt et al, 1993;Röll, 2001;Sakami et al, 2014;Tansley, 1959Tansley, , 1961Tansley, , 1964Zhang et al, 2006), while evidence of rod-to-cone transmutation in colubrid snakes remains somewhat sparse (Schott et al, 2016). In order to demonstrate rod-to-cone transmutation in the retina, there needs to be evidence of a functional rod machinery in a photoreceptor with some rod-like features in a retina that appears, superficially, to consist of only cones.…”

Section: Discussionmentioning

confidence: 99%

Cone-like rhodopsin expressed in the all cone retina of the colubrid pine snake as a potential adaptation to diurnality

Bhattacharyya

Darren

Schott

et al. 2017

Journal of Experimental Biology

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Colubridae is the largest and most diverse family of snakes, with visual systems that reflect this diversity, encompassing a variety of retinal photoreceptor organizations. The transmutation theory proposed by Walls postulates that photoreceptors could evolutionarily transition between cell types in squamates, but few studies have tested this theory. Recently, evidence for transmutation and rod-like machinery in an all-cone retina has been identified in a diurnal garter snake (Thamnophis), and it appears that the rhodopsin gene at least may be widespread among colubrid snakes. However, functional evidence supporting transmutation beyond the existence of the rhodopsin gene remains rare. We examined the all-cone retina of another colubrid, Pituophis melanoleucus, thought to be more secretive/burrowing than Thamnophis. We found that P. melanoleucus expresses two cone opsins (SWS1, LWS) and rhodopsin (RH1) within the eye. Immunohistochemistry localized rhodopsin to the outer segment of photoreceptors in the all-cone retina of the snake and all opsin genes produced functional visual pigments when expressed in vitro. Consistent with other studies, we found that P. melanoleucus rhodopsin is extremely blue-shifted. Surprisingly, P. melanoleucus rhodopsin reacted with hydroxylamine, a typical cone opsin characteristic. These results support the idea that the rhodopsincontaining photoreceptors of P. melanoleucus are the products of evolutionary transmutation from rod ancestors, and suggest that this phenomenon may be widespread in colubrid snakes. We hypothesize that transmutation may be an adaptation for diurnal, brighter-light vision, which could result in increased spectral sensitivity and chromatic discrimination with the potential for colour vision.

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“…A light-induced increase in input resistance has been described also in rod cells of the gecko (Toyoda et al 1969). These cells, however, are said to represent transmuted cones (Walls, 1963;Tansley, 1964) and may not share the properties of rod cells in other retinae. In the frog, osmotic experiments indicate that light reduces the sodium permeability of isolated rod outer segments (Korenbrot & Cone, 1972), but electrical measurements on the same material fail to reveal the expected increase in surface membrane resistance (Falk & Fatt, 1973).…”

Section: Introductionmentioning

confidence: 99%

Light‐induced resistance changes in retinal rods and cones of the tiger Salamander

Lasansky¹,

Marchiafava²

1974

The Journal of Physiology

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3. Values of input resistance were derived from the voltage displacement induced by constant current pulses in darkness or at the peak of the photoresponse. The input resistance following illumination was also calculated from the effect of steady polarizing currents on the amplitude of the photoresponse.4. In darkness, the input resistance of the rod cells is time-and voltagedependent, but the voltage-current relations of most cells have a linear region which includes the physiological limits of membrane potential. At the peak of the photoresponse, the input resistance (slope of the linear region of the v-i relations) is decreased.5. Cone cells show approximately linear v-i relations. As reported by previous authors, illumination increases the input resistance.6. These results support the current view that the cone photoresponse is the consequence of a reduction in the permeability of channels which in darkness shunt the membrane. In rods, however, it appears that the main effect of illumination is to increase the permeability of the membrane to ions for which the equilibrium potential is more negative than the membrane potential in darkness.

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The gecko retina

Cited by 39 publications

References 13 publications

Shedding Light on Serpent Sight: The Visual Pigments of Henophidian Snakes

Shedding Light on Serpent Sight: The Visual Pigments of Henophidian Snakes

Cone-like rhodopsin expressed in the all cone retina of the colubrid pine snake as a potential adaptation to diurnality

Light‐induced resistance changes in retinal rods and cones of the tiger Salamander

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