Anyway, for most fish, reproduction occurs when the sight of a brightly colored male triggers females with fertile eggs to start releasing them. In cichlids, females incubate the eggs in their mouths. Normally, sperm released into the water by a male nearby will fertilize the eggs.
Ah, but in some species of East African cichlids, females are "encouraged" by oval yellow markings found on the anal or pelvic fins of the male. These resemble eggs and when a female approaches the male, she tries to vacuum it up in her mouth --- and gets a mouthful of sperm in the process.
Walter Salzburger at the University of Lausanne, Switzerland led the study, and his team identified the gene, csf1ra as the "culprit." DNA samples from 19 cichlid species, nine with egg spots on their fins and 10 that did not, showed that the species that had evolved most recently had a mutation in the csf1ra linked to the egg spots.
Salzburger says this shows that the dummy egg spots are a genetic trait that provides a selective advantage because they encourage females to participate in oral copulation.