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The secrets of the masquerading butterfly are revealed

By Will Dunham

WASHINGTON (Reuters) - The masquerade party never ends for these ladies.

The females of an Asian swallowtail butterfly species known as the Common Mormon often mimic the appearance of another species of butterfly that is toxic for predators to eat, with strikingly similar coloration and markings on the wings.

This bit of evolutionary skullduggery tricks birds that otherwise would be happy to munch these insects but instead keep them off the menu, thinking they are inedible.

Scientists long have studied this type of mimicry in nature and pondered the biological mechanisms behind it. In the case of the masquerading Common Mormon, the mystery has been solved.

Researchers led by Marcus Kronforst, a professor of ecology and evolution at the University of Chicago, said on Wednesday they have identified the gene responsible for the mimicry in these butterflies.

It is a gene called "doublesex" that already was known to control the development sex-specific attributes in insects.

Kronforst said many experts had assumed that something as complex as this mimicry would be controlled by multiple genes.

"We, in fact, find that it's just one gene," Kronforst, whose findings were published in the journal Nature, said in a telephone interview. "We're just really thrilled to have a clean answer to the question."

The imposter butterflies are engaging in what's known as "Batesian mimicry," named after 19th-century naturalist Henry Walter Bates, who first described it after studying butterflies in South America. His contemporary Charles Darwin's theory of natural selection - sometimes called "survival of the fittest" - helped guide Bates in his observations on insect mimicry.

"Batesian mimicry is the amazing phenomenon where a perfectly harmless creature resembles a dangerous, noxious or poisonous species," Sean Carroll, a professor of molecular biology and genetics at the University of Wisconsin who was not involved in the study, said by email.

"It was a very important discovery because it was obvious evidence for natural selection - the harmless species gains an advantage by resembling something predators avoid - right after the publication of Darwin's theory," Carroll added.

There are numerous examples of such mimicry in nature.

The milk snake is harmless but boasts the same coloration and patterning as the deadly coral snake. Similarly, the hoverfly is harmless, but its yellow markings make it look like a yellowjacket wasp or a bee.

The Common Mormon butterfly, whose scientific name is Papilio polytes, is widely distributed throughout South and Southeast Asia. Its males do not mimic the appearance of other species, but many - although not all - of its females do.

Four different wing patterns appear among the female Common Mormon. One of the patterns resembles that of the male of the species. The other three mimic the wing pattern of three other awful-tasting species, with qualities like a big round patch of white and a bunch of red splotches.

"They are totally delicious," Kronforst said of the Common Mormon, speaking from the perspective of a butterfly predator. "But they have evolved to look like those toxic butterflies essentially to fool predators and avoid predation."

In searching for the gene or genes responsible for mimicry, they compared the genetic blueprint, or genome, of the females that did not mimic other species to the females that did mimic, and were able to narrow the suspects to five genes.

Further study definitively pointed to "doublesex."

(Reporting by Will Dunham; Editing by Jonathan Oatis)

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