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Many species have developed deceptive appearances to fool would-be predators by taking on the look of other unpalatable species. This evolutionary strategy provides an innovative form of extra protection for both groups, but researchers have wondered just how, genetically, crafty mimics pull off such a trick.
A new study, published online August 14 in Nature (Scientific American is part of Nature Publishing Group), shows how one impressive butterfly, the numata longwing (Heliconius numata), is able to switch the patterns on its wings to match those found on local Melinaea butterflies, which taste bad to potential bird predators.
"This phenomenon has puzzled scientists for centuries—including Darwin, himself," Richard ffrench-Constant, a professor of molecular natural history at the University of Exeter and co-author of the new paper,said in a prepared statement. "It was the original observations of mimicry that helped frame the concept of natural selection. Now we have the right tools we are able to understand the reason for this amazing transformation."
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The researchers found that at least 18 genes in a tight area on one chromosome combine to create a so-called "supergene" that functions as a single switch to control wing pattern mimicking and create as many as seven different appearances. "We were blown away by what we found," Mathieu Joron, of the National Natural History Museum in Paris and co-author of the paper, said in a prepared statement. Other supergenes have been located in plants and other animals, but the new find adds evidence to the theory that the elements of supergenes are, indeed, found in close proximity.
"These butterflies are the 'transformers' of the insect world," Joron said. "But instead of being able to turn from a car into a robot with the flick of a switch, a single genetic switch allows these insects to morph into several different mimetic forms," he said, calling it "the stuff of science fiction."
This mechanism for rapidly adaptable change has also been found in other species. "This supergene region not only allows insects to mimic each other, as in Heliconius, but also to mimic the soot blackened background of the industrial revolution," as in the classic peppered moth example, ffrench-Constant said. "It's a gene that really packs an evolutionary punch."
The researchers now hope to find the sites within the chromosomal region and learn how the area works in other closely related species. "We are starting to understand how this switch can have such a pervasive effect," Joron said.
