A passionflower (above) and one of his genetically identical brothers. Photo: Mathieu Chouteau
Reading Birds like to eat butterflies? some species, however, only once: Some insects have found ways to become inedible, and also announce that by a striking wing coloring. Other butterfly species have not developed such defensive tactics themselves. However, they are rarely on the birds' diet because they have done something different: they mimic the wing patterns of various inedible butterfly species from their neighborhoods. It is particularly colorful drives a certain kind of passion flower, in which several pattern imitations occur. A European research team has now discovered how the butterflies manage to produce different patterns despite the same genetic makeup: they use three different variants of a particular chromosome that has a "supergene"? a cluster of different genes that always occur in certain combinations. Even Darwin broke his teeth on this question: How did butterflies with inedible butterflies do for birds, similar wing patterns? usually orange to red with black? to develop? The team headed by Mathieu Joron has now come closer to answering this question with a little detour: The researchers studied genetic material from butterflies that take advantage of the play of colors of the little-tasting neighbors so as not to be eaten themselves.

Surprisingly, despite the very different patterns, the imitators were dealing with the same species? Heliconius numata, a subspecies of the passion flower butterfly, discovered the scientists. The genetic material is almost identical. There is, however, one peculiarity: a particular part of one of the chromosomes harbors a so-called supergene, which determines its external appearance. These are actually a whole group of genes, but always work together in certain combinations and behave accordingly as a single gene. For example, if the gene for the wing tips has the expression "black", the gene for the inner surfaces always sets the color? Red? firmly.

However, this strategy does not always lead to success: patterns that do not protect against predators, ie are only bad copies of the desired colorations, can not prevail? their carriers are simply eaten and do not continue to grow. On the other hand, three patterns in the Passiflora butterflies seem to have proven their worth, because the scientists found three different variants of the chromosome on which the supergene is found? each equipped with a different expression.

"These butterflies are the Transformers of the insect world, " enthuses Mathieu Joron of the Muséum National d'Histoire Naturelle in Paris, alluding to the popular toy action figures. "However, they do not turn from car to robot in an instant, but a single genetic switch allows them to embody several different imitations? that's stuff for science fiction. And only now do we begin to understand how this switch can have such a comprehensive effect. "Display

Already in April 2011, a research group from the University of Liverpool described a similar phenomenon in moths: The butterflies developed during the industrial revolution in England their almost black wing color? a perfect camouflage against sooty walls. Butterflies adapt not only to their own species, but also to their environment if it is for survival. The researchers' conclusion sums up Richard ffrench-Constant from the University of Exeter, UK: "This supergene is really an evolutionary bang."

Mathieu Joron (Muséum National d'Histoire Naturelle) et al .: Nature, doi: 10.1038 / nature10341 wissenschaft.de? Marion Martin

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