|Organization of the ganglion cell layer in the retina of the South-African fur seal adopted to ambivalent vision
Mass A.M.1, Supin A. Ya.1
1 Severtsov Institute of Ecology and Evolution, RAS
Retinal topography, cell density, distribution, and sizes of ganglion cells in the retina of the South-African fur seal (Arctocephalus pusillus (Otariidae) were analyzed in retinal wholemounts stained with cre-syl-violet. Main types, number, and sizes of ganglion cells were identified. Some features were found in common with both terrestrial and marine mammals. Maps of ganglion cell density distribution were composed. A specialized area of high concentration of ganglion cells were found. This area was located in the temporal retinal quadrant, 9-10 mm (23-25°) from the optic disk. Localization, size and configuration were similar to the area centralis of terrestrial carnivores. In different wholemounts, the peak cell density in the high-density area ranged from 900 to 1200 cells/mm 2 (mean 1020 cells/mm 2). With a posterior nodal distance of 23 mm (underwater), this mean density corresponded to 164 cells/deg 2. These values predict a retinal resolution of 4.7' (6.3 cycles/deg) in water and 6.3' (4.7 cycles/deg) in air. A distinctive feature of the fur seal's retina is the large size of ganglion cells as compared to terrestrial mammals. The ganglion cell diameter ranged from 8 to 37 urn. The cell-size histograms featured groups of small and large ganglion cells. These large cells constituted a few percents of the total ganglion cell population.
SOUTH-AFRICAN FUR SEAL, GANGLION CELLS, TOPOGRAPHY, RETINA, WHOLEMOUNT, CELL SIZES, HIGH-DENSITY AREAS