The Distribution and Size of Retinal Ganglion Cells in Microcebus murinus, Cheirogaleus medius, and Tarsius syrichta: Implications for the Evolution of Sensory Systems in Primates

Abstract

Sensory specializations, particularly in the visual system, have been crucial factors in the evolution of brain and behavior in primates (Allman, 1998; Kay and Kirk, 2000; Ross, 2000). The entire output of the retina is channeled through the retinal ganglion cells whose axons form the optic nerve connecting the eye and brain. The patterns of retinal ganglion cell density and size in anthropoids are different from those in strepsirrhines known to date ( Otolemur cmssicaudatus and Galago senegalensis). Anthropoids have higher ganglion cell densities in the central retina than these strepsirrhines, and exhibit a marked gradient in cell soma size across the retina, with larger cells in the periphery of the retina. In the absence of data on these parameters in a wider range of strepsirrhines and haplorhines, it is impossible to determine whether these differences are due to broad ecological differences between the groups, such as activity pattern, or to less tractable suborder differences in visual system anatomy.