Evolution of multiple retinal rod pigmentation Ryan Adams Psychology 159
Origins of color vision • Evolved 700 million years ago • Australian lungfish (Neoceratodus forster) • Southern hemisphere lamprey (Geotria australis) • Chondrichthyes (sharks and rays) • Non-Actinopterygia (early ray-finned fish)
Evolution of pigment Ostracoderms • Two theories • Two pigments. One to match the background, and another to offset. Able to detect targets spectrally different from the background. • Two pigments. In order to eliminate noise created by flicker of light over surface of water. Allowing for earlier detection of predators.
Southern Hemisphere lamprey • Representative of the earliest vertebrates.
Lamprey Three of five photo pigments Upstream Yellow/orange has major effects on the green wavelength receptors. Downstream
Evolutionary reasons • Dates back at least 540 Million years • Five major types of cone opsins • Each very different Shallow water. Ability to see colors allows for greater exploitation of the surrounding environment.
Other animals • Rodents are sensitive to UV light • Hummingbirds are sensitive to near-UV light • Goldfish have UV-sensitive cones
References The origins of color vision in vertebrates. Clin Exp Optom 2004; 87:4-5:217-223. More than three different cone pigments among people with normal color vision. Neitz J, Neitz M, Jacobs GH. Department of Cellular Biology and Anatomy, Medical College of Wisconsin, Milwaukee 53226.
Humans • A fundamental feature of normal color vision is that red and green lights can be mixed to appear identical with a monochromatic yellow light. Another characteristic of normal color vision is that people often disagree on the amounts of red and green needed in the mixture to exactly match the yellow. Comparison of such color vision differences with photopigment gene differences reveals that a serine/alanine polymorphism at amino acid position 180 of X-encoded pigments can account for this type of color vision variation. This amino acid change shifts the spectrum of the pigment produced by about 6 nm, a value that would predict a larger minimum color vision difference between individuals than is actually observed. This discrepancy can be explained if, counter to the Young-Helmholtz theory as the explanation of trichromacy, many people with normal color vision have more than three spectrally different cone pigments.