Butterfly Evolves Leg Up on Male-Killing Parasite

July 12, 2007

The continuing battle between a butterfly and the bacteria that nearly wiped out all the insect species' males has taken a sudden and unexpected turn.

In just a few years, the butterfly has evolved a way to evade the bacteria's tightly controlling grip.

The findings show that evolution can strike in a flash, even after long periods of time with little change, researchers say.

For at least a century, according to the experts, bacteria called Wolbachia had been playing puppet master with Hypolimnas bolina butterflies found on two Samoan islands (see an Oceania map).

The bacteria had been killing off nearly all the male larvae of the butterfly, also known as the eggfly or the blue moon butterfly.

But males made a comeback in 2006, the researchers found, with nearly as many of them as females.

"We thought this kind of thing was happening, but we didn't know we'd be lucky enough to see it," said Sylvain Charlat of the University of College London, one the researchers involved in the new study.

The shift happened in five years or less—just ten generations for the butterflies—according to the new study, which will appear tomorrow in the journal Science.

This is a "very, very fast evolutionary change, possibly the fastest ever monitored," Charlat said.

Bonanza of Females

In the early 20th century, some visitors to Polynesian islands noticed that, curiously, there were hardly any eggfly males.

Later, researchers discovered that Wolbachia, one of the world's most common insect parasites, was the culprit. Wolbachia invade reproductive systems, allowing the bacteria to control insect development. (Related: "Suicide Grasshoppers Brainwashed by Parasite Worms" [September 1, 2005].)

Continued on Next Page >>




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