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PR Robinson, LA Newman; An Investigation of the Color Vision of Marine Mammals . Invest. Ophthalmol. Vis. Sci. 2002;43(13):4544.
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© ARVO (1962-2015); The Authors (2016-present)
Purpose: It has long been hypothesized that the visual systems of animals are evolutionarily adapted to their visual environment. The entrance many millions of years ago of certain mammals into the sea gave these new marine mammals completely novel surroundings with respect to light availability and predominant wavelengths. This work examines the color vision of the marine mammals, predicting that the deep-dwelling animals will not have color vision. Methods: Cone opsin genes from two orders (Cetacea and Sirenia) and an additional suborder (Pinnipedia) of marine mammals were amplified by PCR, cloned and sequenced. Genes considered to be functional were cloned from retinal cDNA. These genes were inserted into an expression vector and expressed in COS-7 cells. Opsin proteins were reconstituted with the 11-cis-retinal chromophore, purified, and lmax values determined. Results: All animals studied from the order Cetacea have SWS pseudogenes, whereas a representative from the order Sirenia has an intact SWS gene, which should be expressed in the retina. One of the pinnipeds studied (Harp seal) had a SWS pseudogene, whereas another species (Harbor seal) appeared to have an intact SWS gene, but upon further examination, no message was found in the retinal RNA, suggesting a promoter or splice site mutation rendering the gene inexpressible. Preliminary data shows that the LWS opsins of the Cetaceans studies are all blue-shifted (compared to the bovine LWS opsin) by at least 30nm. The LWS opsin of the single Pinniped studied has lmax similar to that of terrestrial mammals, and the manatee has a LWS opsin which is red shifted from those of terrestrial mammals. Conclusion: These findings support our hypothesis; in the monochromatic oceanic habitat, the pressure to maintain color vision is removed, and mutations are retained in the SWS genes, resulting in pseudogenes. The remaining LWS opsins are blue-shifted in their lmax in order to adapt to the bluer light in the deep ocean. In contrast, the manatee result suggests that certain aspects of the lifestyle (possible herbivory) of this species require color vision. The Pinnipeds represent an intermediate stage of color vision evolution: they have lost their SWS pigment but have not yet blue-shifted their remaining LWS opsin.
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