The gaudy brown Brazilian butterfly known as Heliconius numata has long puzzled geneticists. It has seven different wing patterns, each of which mimics that of a different local species of Melinaea, another group of butterflies...Further details at the Nature and NYT links. Via the February 2013 issue of Badger Butterflyer, the outstanding newsletter of the Southern Wisconsin Butterfly Association.
To help perfect their imitation of the seven Melinaea models, the butterflies have
somehow locked what should be a continuous range of natural variation into seven specific patterns...
But how do the Heliconius butterflies pull off the trick of having seven different forms in a single interbreeding population? Each wing pattern is specified by many different genes, but since genes get shuffled in each generation, the different wing patterns should quickly merge together when parents with different wing patterns mate.
A team of French and British biologists, led by Mathieu Joron of the National Museum of Natural History in Paris, has discovered the butterfly’s solution. It has locked together in a supergene a cluster of 18 genes involved in specifying the wing pattern. The supergene is inherited as a single unit, the biologists report in the current issue of Nature.
For the enthusiast, there is also an explanatory video.