Organisms often come up with the same evolutionary solution to thrive in a niche environment. For example, observe the matching colors among the bugs and butterflies that feed on the common milkweed and its relative dogbane. But for milkweed-eaters, this parallel evolution is more than skin-deep: A study of 14 of these insect species—from three insect orders and spanning 300 million years in evolution—shows that this repeatability occurs on a molecular level. Milkweed produces a toxin that disables a key protein in the animals that eat these plants; this protein helps transport ions that are important for muscle contraction, neural function, and other cellular processes. To get around this toxin, most of these milkweed-eating insects have undergone the same set of genetic mutations that alter the protein so the toxin can't stick to it. Meanwhile, four other insect species independently found a different work-around: Instead of altering the protein, these insects duplicated the protein's gene. That way, the original protein can still do its job of transporting ions—and the extra copy is free to change its amino acid sequence in a variety of places to make these species resistant to the toxin, researchers report online today in Science. With so many distantly related insects finding the same genetic routes to milkweed tolerance, the team concludes that evolution is repeatable—although gene duplication can also open up new evolutionary opportunities.
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