Cellular mechanisms for color-coding in holostean retinas and the evolution of color vision.

Electrophysiological recording and microspectrophotometry were used to analyze retinal function in representatives of the two surviving genera of holostean grade fish--the bowfin (Amia calva) and gars (Lepisosteus sp.). The properties of the cone photopigments, horizontal cells and ganglion cells show that these holostean retinas have cellular mechanisms for color vision which are fundamentally similar to those previously described for teleosts, turtle and mammals. These findings suggest that trichromatic receptor systems and opponent color-coding mechanisms may have evolved in primitive Neopterygii or more ancient fish, before the advent of teleosts. In conjunction with other recent data on living representatives of primitive fishes, these findings also add renewed plausibility for the view that vertebrate color vision could have taken a common origin some 400 million years ago from an ancestral aquatic jawed vertebrate.