Butterflies make use of mimicry ‘supergene’

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 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.

Supergenes are widespread in nature and account for a multitude of visual features, from the shape of primrose flowers to the colour and 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.

Prof 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.”