Comparative scaling analyses of mammalian eye size and brain size

Abstract

Studies of the relative sizes of brain components in mammals suggest that areas responsible for sensory processing, including visual processing, are correlated with aspects of ecology, especially diet and activity pattern. However, mammalian eye shapes and sizes do not display similar adaptations to ecological factors. This disparity in ecological adaptations between eye and brain size is especially surprising given the importance of activity pattern, a correlate of light availability, to eye morphology in most other vertebrate classes. Current data suggest that an isometric scaling relationship best describes eye to brain size size scaling in mammals. In this study, we compile the most taxonomically diverse and extensively sampled dataset on eye size and shape, overall brain volume, and activity pattern, in mammals. Results demonstrate that eye and brain sizes are correlated, although regression slopes do not support an isometric relationship. Anthropoid primates are important outliers, demonstrating adaptive size and shape differences in eye morphology. We conclude that in mammals allometry more strongly affects eye to brain size scaling than do ecological factors.Grant Funding SourceMidwestern University