| Most animals cannot eat milkweed, which contains a toxin that turns stomachs in small doses and can be lethal in larger ones. A few species, though, thrive on the plant. Young monarch butterflies, as caterpillars, only eat milkweed. This noxious diet makes their bodies unpalatable to birds, frogs and other predators. Milkweed should make fruit flies sick, too. But in the hands of a team of biologists, as a study out today in Nature shows, fruit flies can be engineered to eat the plant. The geneticists manipulated a fly gene at three locations to mirror the monarch version. This tweak allowed the flies to munch away on a milkweed diet. "Monarch flies," as the scientists called them, tolerated the toxin as easily as their namesake butterflies. When the maggots transformed into adult flies, their bodies stored some of the milkweed toxin — as do the monarch caterpillars that go through metamorphosis. This is the first time, per the scientists, that a set of evolutionary mutations has been completely re-created in animals, giving them a new diet and a new defense mechanism. "All we did was change three sites, and we made these superflies," said study author Noah Whiteman, an expert in integrative biology at the University of California at Berkeley, in a statement. "But to me, the most amazing thing is that we were able to test evolutionary hypotheses in a way that has never been possible outside of cell lines." This technique allowed the scientists to pinpoint the three sites responsible for the monarch's adaptation to milkweed. Other insect species can also tolerate milkweed, though not as well as the butterflies. These insects evolved mutations at the same three sites Whiteman and his colleagues studied. "It would have been difficult to discover this without having the ability to create mutations with CRISPR," Whiteman said. That gene-editing tool has, in recent years, created all kinds of new mutants, such as albino lizards and butterflies with new wing patterns, and it altered cloned monkeys. |
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