Take a look at the photo above. Contrary to their appearance, these two butterflies are actually very different. Erato demophoon and Melpomene rosina diverged 11 million years ago, about the same time our fate diverged from that of the orangutan. But unlike humans and their distant primate cousins, after being apart for five million years, the two insects underwent convergent evolution, resulting in those two red and yellow stripes on black wings. In the March 10 issue of the newspaper Science, an international team looked into the genomes of the two species of butterflies and some other closely related lepidopterans. The results they achieved are quite something.
The genes Heliconius is well known to butterfly lovers. Since the work of the 18th-century Swedish zoologist and taxonomist Carl Linnaeus, along with, in particular, the great naturalists of the 19th century like Charles Darwin, Henry Walter Bates, and Otto Friedrich Müller, scientists have been delighted by the variety of colors and patterns that its 48 species and hundreds of subspecies display on their wings. But this variety includes similarities in far-apart species. What is even more surprising is that two subspecies from two different species, as is the case here (the species being Erato and Melpomene and the subspecies being demophoon and rosina) can present a much closer phenotype than two different subspecies within the same species.
Researchers thought they knew the reason for this convergent evolution: The color of the wings (black, yellow and red) is carried by three genes. Even if these two species differ greatly in their genome, these three elements appear identical. The study published in Science put this similarity into perspective by pointing out that the genes are indeed identical, but their expression profiles are completely different.
Two advanced research techniques
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To demonstrate this, researchers combined two state-of-the-art techniques. The first, ATAC-Seq, identifies areas of the genome likely to host promoters of the famous wing color genes. Located at a distance of about two thousand bases from the genes, these kinds of switches do not code the proteins that will give a red, yellow, or black color, but they regulate the expression of the three genes in the tissues. In both species of butterflies studied, the team saw different areas appear. This was the first time this technique was used in this type of study.
But did these areas actually host the famous switches? To prove so, the scientists used Crispr/Cas9 technology, allowing them to switch off one gene at a time. In this way, they found which ones played a decisive regulatory role.
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