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P.K. Ahnelt, A. Schiviz, C. Schubert, A. Kuebber–Heiss; Retinal Cone Topography of Hoofed (Artiodactyle) Mammals . Invest. Ophthalmol. Vis. Sci. 2006;47(13):2846.
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© ARVO (1962-2015); The Authors (2016-present)
In this comparative study we have gathered the spectral cone photoreceptor mosaics from hoofed mammals to compare their topographies and detect possible correlations to specific lifestyle, habitat and physical parameters.
Eyes from 25 artiodactyle species including cow, gazelles, giraffe, pudu, deer, barbary sheep, kantchil were collected in Austrian animal parks and zoos and from a certified hunting farm in Namibia. Spectral cone subpopulations were identified and mapped using anti–opsin antisera.
In all species examined two classes of cones were detected. The standard–distribution of M–cones, as also found in the cattle, is L–shaped: a horizontal visual streak, includes a temporal area centralis has a dorso–temporal extension of higher cone density. Variations of this L–shape were found to be highly dependent on the animal's height – very small animals tend to have a visual streak only, very large species show a near complete arch of higher densities. A significant correlation with specific habitats could not be proved except for mountaineous species and dense–forest dwellers which tend to have peripherally enhanced S cone densities. Effects of domestication in cow versus related species and of phylogenetic proximity (irrespective of ecotypes) were not detected. As found in other mammals, S–cone proportions are 5 – 30 % depending on species and retinal location. S–cones show a broader variation in their topographical distribution and which seems correlated with body height, and habitat. Their distribution is not coupled to the M–cone streak. Maps commonly show increased densities temporally and dorsally of the optic nerve. In 2 small species however, maximum densities are situated ventrally. For the cow no effects of domestication with respect to distribution and density were detected.
As indicated by the visual streak the plantivore artiodactyles are primarily adapted to open habitats but variants in peripheral distribution of both, M– and S–cones, suggest significant modificatory effects from eye height and structure of the environment.
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