Color Vision in Marine Mammals: A Review

Marine mammals present a unique opportunity to study the course of evolutionary development of visual processes in their adaptation from a terrestrial to an underwater environment. The ambient light conditions in the oceans differ considerably from those on land and pose different challenges to the visual system. The optic mechanisms and the retinal structures of the eyes of marine mammals show specific adaptations for vision in both media. The present review delineates the environmental conditions of life in the ocean that have shaped the color vision systems in the various marine mammals. Recent findings have shown that cetaceans and pinnipeds have a very unusual visual system among the mammals because they seem to have lost their short-wavelength-cones completely. Nevertheless, behavioral data indicate that all three groups of marine mammals discussed here (cetaceans, pinnipeds, and manatees) are able to discriminate colors. A possible underlying mechanism for color vision in pinnipeds and cetaceans could be based on the comparison of rod and cone signals.