A team of international researchers led by Luca Livraghi at the George Washington University and the University of Cambridge has uncovered a surprising genetic mechanism that influences the vibrant and complex patterns on butterfly wings. In a study published in the Proceedings of the National Academy of Sciences, the team discovered that an RNA molecule, rather than a protein as previously thought, plays a pivotal role in determining the distribution of black pigment on butterfly wings. This discovery challenges long-standing assumptions about genetic regulation and opens up new avenues for studying how visible traits evolve in animals.
The genetic code contained within the cells of developing butterfly wings dictates the specific arrangement of the colors on the wing’s scales, similar to the arrangement of colored pixels to form a digital image. Researchers observed that manipulating the genetic code in butterflies with gene-editing tools can have a direct effect on visible traits, such as coloration on a wing. While scientists have long known that protein-coding genes are crucial to these processes, the team’s research revealed that an RNA molecule controls where dark pigments are made during butterfly metamorphosis.
Using the genome-editing technique CRISPR, the researchers demonstrated that when they removed the gene that produces the RNA molecule, butterflies completely lost their black pigmented scales. This showed a clear correlation between RNA activity and dark pigment development. This gene acts as an “evolutionary paintbrush,” shaping the butterfly’s color patterns in unexpected ways. The researchers observed a perfect correlation between where the RNA is expressed and where black scales eventually form on the wing, indicating its crucial role in color pattern development.
Further research explored the function of the RNA molecule in several other butterfly species whose evolutionary history diverged around 80 million years ago. In each of these species, the RNA had evolved to control new placements in the patterns of dark pigments. The consistent results obtained from CRISPR mutants in multiple species demonstrate that this RNA gene is not a recent invention but a key ancestral mechanism to control wing pattern diversity. The study also revealed that this same RNA gene is used across different butterfly species, from longwing butterflies to monarchs and painted lady butterflies, indicating its importance in the evolution of wing patterns.
The findings of this study have broad implications for the field of genetics and evolutionary biology. The discovery of the RNA molecule’s role in determining color patterns on butterfly wings challenges previous assumptions about genetic regulation and sheds light on a previously overlooked aspect of the genome. The research opens up new avenues for studying how visible traits evolve in animals and highlights the importance of exploring the “dark matter” of the genome. By uncovering the intricate genetic mechanisms underlying butterfly wing patterns, this study enhances our understanding of how genes build anatomy and how traits evolve in the animal kingdom.