For the few flashy, colorful male African cichlid fish, life is good. They control food, females and territory, and all the other fishies must follow their lead.
But 80 percent of the population is comprised of low-ranking males, dull-grey in color who must compete with the females to find food.
A team of Stanford researchers set out to see why some fish flourish, while the others flounder, discovering that changes in the expression of the cichlid's genes, known as epigenetic changes, are responsible. In particular, a process called methylation adds methyl molecules to genes, controlling their expression. From the Stanford News release:
"Status differences exist in all social organisms," said Russell Fernald, a biology professor at Stanford University and senior author of the study. "Our work reveals how social dominance status is possibly regulated through methylation, which is important because individuals higher in rank generally enjoy better health and quality of life."
Fernald and his team manipulated the fish in his lab to directly test their hypothesis:
Several pairs of non-dominant males matched in size were each placed in an aquarium that could support only one territory. In each pair, one male was injected with a methylating agent while the other received a methylation suppressor, and the two fish fought for dominance.
"We could see the behavioral change in a matter of minutes, as one animal began to dominate the other," Fernald said. "Videos of these confrontations showed that the fish injected with the methylating agent were much more likely to be the winners, while those receiving the methylation suppressor typically lost the fight for dominance.
"It was remarkable that we could determine which fish became dominant by changing the range of genes expressed in this context," he said.
The release also explains the cichlids' quirky mating process, which requires the male to fool the female by flashing a fin covered with egg-like spots. Thinking she dropped her eggs, the female tries to collect them, gathering sperm in the process.
For more, check out the study in PLoS ONE.
Previously: Using epigenetics to explain how Captain America and the Incredible Hulk gained their superpowers, A tiny fish helps solve how genes influence longevity and My funny Valentine — or, how a tiny fish will change the world of aging research
Photo by L.A. Cicero