How Evolution Creates New Traits, Like Colorful Cichlid Fish Egg-Spots

Evolution is constantly churning out new traits with novel functions. But what causes this process to occur in the first place? By studying the color markings of cichlid fish, scientists have figure out what triggers these evolutionary innovations.

Biological evolution is based on the progressive adaptation of traits through natural or sexual selection. Every so often, though, complex traits with completely new functions develop; for example, when insects developed wings. Yet what causes these new traits to arise has long been a source of controversy. That's why scientists decided to look at the process of evolution a bit more closely.

In this case, they took a look at African cichlids. The males of over 1,500 species of these fish feature conspicuous color markings on their anal fins, called egg-spots. These spots play an important role in the mating behavior of these fish. After spawning, the female gathers up her eggs in her mouth before fertilization. Then, the male presents his egg-spots and the female brings her mouth, with the eggs, close to the male's genital opening.

When it comes to the cichlid's egg-spots, the researchers found that the presence of "jumping genes" were to blame. This mobile genetic element is located upstream of a pigmentation gene with the name fhl2b. This, in particular, causes an alteration in gene expression in pigmentation cells which results in the development of the egg-spot pattern.

"These results illustrate once more the importance of changes in gene expression in evolution," said Walter Salzburger, one of the researchers, in a news release.

The findings reveal the importance that jumping genes have to play when it comes to evolution. More specifically, it shows how this particular trait developed in these fish. This, in particular, reveals a bit more about the process of evolution.

The findings were published in the journal Nature Communications