Guppy Love: Guppy mate choice changes the way they see color

Most people have a favorite color. But could that color have anything to do with who you’re attracted to? Researchers studying the Trinidadian guppy, a small fish found only on Trinidad, think it might.

Color vision is usually thought to be consistent across species; they either have it, or they don’t. But research on the opsin proteins of guppies may change that assumption. Opsin is a protein in the cone cells of eyes, and it determines what wavelengths of light are absorbed. In other words, what form of opsin is expressed changes which colors are seen. Humans only have three opsin types, but guppies have nine. That means they see a much broader range of color than we do.

In Trinidad, an island off the coast of Venezuela, small pools of water form isolated environments of guppies that have no contact with each other. This makes a perfect environment to study different populations with different needs based on what’s around them. In one pool there’s high predation of guppies, while in another, there are relatively few animals who’d like guppy for lunch. Guppies naturally like the colors red and orange, so when there’s no reason not to be seen, the males show it off to attract a female. But in high predation pools, males damp down their coloration to be less noticeable. Females in high predation pools tend to mate with these drab males so that their children are less likely to be eaten.

But how do they make this choice, assuming they don’t understand genetic heritability? Researchers wondered if the way guppies see color could explain the difference in preference seen in these two environments. They hypothesized that guppies in low-predation pools would have more opsin expression for red and orange light, and therefore be able to see bright colors and flashy patterns on males. If this were true, then it would mean female guppies actually saw mates differently according to their environment. To answer this question, researchers looked to see how much of each type of opsin was expressed in the DNA of fish from each population. When they compared the amounts between the low and high predation pools, there was a clear difference.

As they predicted, females in low-predation environments saw more red and orange colors. This was reflected in their very DNA with what form of opsin was present. In high-predation pools, females wouldn’t mind that there were no brightly colored males, because they can’t see the colors anyway. This debunks the assumption that different populations of a species all see the same way.

What could this mean for human populations? We all know that beauty is in the eye of the beholder, but it turns out that might be far more literal than we thought. If guppies see differently according to where they live, people might too. This means that what attracts you is in your DNA: if purple is your favorite color, it might be because your eyes see more purple wavelengths of light than someone else’s. Who knows, it might even affect who you choose to spend your life with.