Abstract
Variable expression of visual pigment proteins (opsins) in cone photoreceptors of the vertebrate retina is a primary determinant of vision plasticity. Switches in opsin expression or variable co-expression of opsins within differentiated cones have been documented for a few rodents and fishes, but the extent of photoreceptor types affected and potential functional significance are largely unknown. Here, we show that both single and double cones in the retina of a flatfish, the starry flounder (Platichthys stellatus), undergo visual pigment changes through opsin switches or variable opsin co-expression. As the post-metamorphic juvenile (i.e., the young asymmetric flatfish with both eyes on one side of the body) grows from ~5 g to ~196 g, some single cones and one member of unequal double cones switched from a visual pigment with maximum wavelength of absorbance, λmax, at shorter wavelengths (437 nm and 527 nm) to one with longer λmax (456 nm and 545 nm, respectively) whereas other cones had intermediate visual pigments (λmax at 445 nm or 536 nm) suggesting co-expression of two opsins. The shift toward longer wavelength absorbing visual pigments was in line with maximizing sensitivity to the restricted light spectrum at greater depths and achromatic detection of overhead targets.
Highlights
Vertebrate photoreceptors contain visual pigments that capture light to begin the process of vision[1]
Such results suggested the contribution of multiple opsins to the S (445) and M (536) visual pigment absorbance curves since analyses of retinal extracts using High Performance Liquid Chromatography revealed the same A1 retinal chromophore as present in younger fish[34] (Fig. 2)
This result indicates that the S (445) visual pigment consisted of two visual pigments: the S (437) and the S (456), the latter bleached by the 480 nm light
Summary
Vertebrate photoreceptors contain visual pigments that capture light to begin the process of vision[1]. Binding of A1 retinal to an opsin will result in a visual pigment with lower wavelength of maximum absorbance (λmax) than conjugation to A2 3,4-dehydroretinal[3] It is the combination of multiple cone photoreceptor types, each expressing a different predominant visual pigment, that determines the colour vision capabilities of an animal[1]. We examined changes in visual pigments of the post-metamorphic starry flounder from the younger (~5 g in weight, total length ~7.5 cm) to older (~196 g in weight, total length ~18–23 cm) juvenile During this period, spanning more than two years of growth, the fish in nature progresses from life in shallow bays (1–20 m in depth) to deeper oceanic waters along the coastal shelf (>20 m in depth)[31]. The visual ecology of the starry flounder (and of flatfishes in general) is very different from that of the few pelagic fishes that have been examined for opsin co-expression
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