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)
