At a bar, intoxicated people may fall victim to the notorious “beer goggles” effect. Now, researchers have discovered that in the fish world, pollution can have the same effect as a six-pack of Heineken.
Scientists already know that female African cichlids are partially blind, and have evolved into a new species over the past 30 years. The cichlids in Lake Victoria’s polluted waters are vanishing, causing “the largest human-witnessed mass extinction of vertebrates.” And now, pollution is also causing closely-related species of cichlids to interbreed, all because they can’t see each other.
Color is very important in cichlid mate choice, and normally when the water is clear, red females like red males and blue females like blue males. Because blue appears brighter in shallow water and red is brighter in deep water, the fish tend to stick to their comfort zones. But when the water is murky, they have no qualms about interbreeding.
Ole Seehausen of the University of Bern in Switzerland used cichlids to test out the sensory drive hypothesis, a theory that new species can arise from senses (in this case, vision). By examining mating behaviors of the fish in laboratory tanks, Seehausen found that the mixed-bred fish went for blue or red fish and did not select their mate based on color. By looking at the “light-detecting proteins” in the genome, Seehausen found that the genes linked to vision evolved faster than the rest of the fish’s genes.
Evolution by vision has occurred in other species as well. After primates evolved to see red for foraging advantages, they started growing red skin and hair. Before long, red skin and hair became a clear sexual preference.