S–cone topography in Old World Primates: Human pattern resembles that of arboreal/forestal rather than (semi–) terrestrial species

Abstract

Abstract: : Purpose: Studies on the tiling of the visual field among diurnal primates including man studied have generally revealed foveo–centric gradients. The present study establishes and analyzes S–cone topographies in man and primates to reveal possible effects of different lifestyles. Methods: Human retinas were obtained from corneal donor eyes and eyes from Pan troglodytes, Macaca sylvatica, M. rhesus, M. fascicularis and Mandrillus sphinx were obtained from veterinary pathology or from unrelated experiments. The isolated retinas were labelled for S–opsin using JH455 (J.Nathans) and N–20 (SantaCruz) antibody. Sampling cone density along orthogonal grids led to the establishment of topographical maps from which the density values were summed along 10° meridians around the foveal center. Plotting the sums as angular vectors the relative weighting of visual field sectors could be evaluated and compared between species. Results: The polar plots derived from the topographic maps demonstrate that the basic pattern of Old world Primate S–cones is concentric with a bias for the nasal meridian. In Man, and to somewhat lesser extent in Chimpanzee, the radial profiles are nearly iso–tropic with only slight horizontal compression (C= vert/hor meridian = 0,9). Among macaques there is a range of vertical /horizontal ratios from M. fascicularis (C=0,85) and M. mulatta (C=0,8) to the mountainous M. sylvatica (C= 0,8 – 0,75). The Mandrill, has S–cones clearly concentrated along the horizontal axis (C= 0,7) in particular in the nasal retina where densities above 600/sqmm are maintained towards the far periphery. Conclusions: The nasal horizontal elongations of (S–) cone densities such as in Mandrill are chracteristic for (semi–) terrestrial animals in open environments (e.g.:antelopes, cheetah, Ahnelt unpubl.). This design is likely to be more suited for spotting/tracking predators and foraging group members (in Mandrill with coloured skins parts). Early hominids are supposed too have evolved in similar habitat scenarios. Thus the highly concentric pattern – resembling that of forestal/arboreal primates – has to be considered a conservative element of human visual system design. Its preservation may be linked with the concurrent transition to bipedism.

Keywords: color vision • photoreceptors: visual performance • retina: distal (photoreceptors, horizontal cells, bipolar cells)