A recent study, published online in the journal Nature, solves an evolutionary mystery—how the Amazonian butterfly species Heliconius numata manages to mimic other butterfly species in the genus Melinaea.
Mimicry occurs frequently in nature, but H. numata does something extraordinary! It mimics the wing patterns of the seven different species of Melinaea exactly, without variation.
The New York Times describes this phenomenon really well:
This genetic trick is as surprising as if people all grew to certain prescribed heights, like 5 feet, 6 feet or 7 feet, with nothing in between.
The mimicry acts as a disguise, protecting H. numata against predators. Melinaea species eat poisonous plants that make them toxic to birds, so H. numata mimics their neighbors to keep the birds away, too. Researchers have known this for years, but not how the H. numata is able to mimic the seven wing patterns genetically.
So a team of European scientists located and sequenced the chromosomal region responsible for the wing patterns in H. numata. The single chromosome contains several genes that control the different elements of the pattern. Known as a “supergene,” this clustering allows genetic combinations favored for their mimetic resemblance to be maintained, while preventing combinations that produce non-mimetic patterns from arising.
Supergenes are responsible for a wide range of what we see in nature: from the shape of primrose flowers to the color and pattern of snail shells.
In addition, the researchers found that three versions of the same chromosome coexist in this species, each version controlling distinct wing-pattern forms. This has resulted in butterflies that look completely different from one another, despite having the same DNA.
“We were blown away by what we found,” said lead author Mathieu Joron of the Muséum National d’Histoire Naturelle in Paris. “These butterflies are the ‘transformers’ of the insect world. But instead of being able to turn from a car into a robot with the flick of switch, a single genetic switch allows these insects to morph into several different mimetic forms—it is amazing and the stuff of science fiction. Now we are starting to understand how this switch can have such a pervasive effect.”
Co-author Richard ffrench-Constant of the University of Exeter added: “This phenomenon has puzzled scientists for centuries—including Darwin himself. Indeed, it was the original observations of mimicry that helped frame the concept of natural selection. Now that we have the right tools we are able to understand the reason for this amazing transformation: by changing just one gene, the butterfly is able to fool its predators by mimicking a range of different butterflies that taste bad.”
Image: Mathieu Chouteau