Butterflies' amazing feat of mimicry explained

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 thereby avoid being eaten.

But how this evolutionary conjuring trick, known as "Mullerian mimicry", occurs has long been a mystery.

Scientists have now 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 is 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 wing's appearance.

The "supergene" clustering allows genetic combinations for mimicry favoured by natural selection to be maintained.

At the same time, combinations that produce non-mimetic patterns are prevented from arising.

Professor Richard ffrench-Constant, from the University of Exeter, one of the researchers who report the discovery in the online edition of the journal Nature, said: "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."