These varieties, artificially generated by the creators, are relatively recent, which allows the mechanisms to have been maintained and not to have been hidden in the genome, says to the Observer Ricardo Jorge Lopes, researcher at Cibio-InBio and author of the magazine's cover photo.
Thus, when the team of Portuguese and American researchers compared the genome of the mosaic canary with that of the other domestic canaries, it was possible to identify where the difference was, that is, which gene was responsible for sexual dichromatism. Later, the researchers found the same gene in other species that show differences between males and females in this type of color.
“BCO2 is the first gene identified as important in sexual dimorphism in birds, more specifically in the differences in color of carotenoids between males and females”, says Ricardo Jorge Lopes, researcher at Cibio-InBio.
The identified gene, BCO2, contains the message that allows the creation of an enzyme that degrades a specific type of pigment, the carotenoids – responsible for the colors between yellow and red. When the gene is turned on, there is more degradation of the pigment, therefore less color accumulated in the feathers. What the researchers found was that mosaic canary females had more active BCO2 genes, therefore fewer red areas or a more faint red.
Moreover, it was possible to verify that turning the gene on or off depends on the hormone estrogen, so the females that no longer reproduced, and did not produce the hormone (like the older ones or without ovaries), had a coloration more similar to that of males – because the gene was turned off.
For the study's authors, this simple genetic mechanism can help explain why carotenoids are the pigments most often associated with sexual dichromatism in birds: just turn a single gene on or off to be able to see the differences right away.