Transformer gene key to copycat butterflies
A single "supergene" allows butterflies to perform feats of mimicry that confused Charles Darwin, research has shown.
Many butterflies adopt wing patterns similar to other species that taste bad to birds, and avoid being eaten.
But how this evolutionary conjuring trick, known as "Mullerian mimicry", occurs has long been a mystery.
Study leader Dr Mathieu Joron, from the Museum of Natural History in Paris, France, said: "We were blown away by what we found. These butterflies are the 'transformers' of the insect world. But instead of being able to turn from a car into a robot, a single genetic switch allows these insects to morph into several different mimetic forms -- it is the stuff of science fiction."
Scientists found the answer by studying the tropical butterfly Heliconius numata, which can resemble several other butterfly species, in the Amazon rainforest.
One population of H numata can sport coloured wing patterns similar to those of other butterflies in the same location that are unpalatable to birds.
The researchers analysed DNA in the genetic code region responsible for butterfly wing patterns.
They found that H numata's wing pattern was controlled by a "supergene" -- a cluster of several genes in one part of a single gene package, or chromosome.
Together, these genes control different elements of the appearance of the butterfly's wing.
This allows for mimicry favoured by natural selection to be maintained.
At the same time, combinations that produce non-mimetic patterns are prevented from arising.
Supergenes are widespread in nature and account for a multitude of visual features, from the shape of a primrose to the pattern of snail shells.
Three versions of the same chromosome co-exist in H numata, the scientists found. Each give rise to an array of distinct wing pattern forms. This makes it possible for individual butterflies to look completely different from one another despite having the same DNA.