Male butterflies swiftly out-evolve killer bacteria

Berkeley researchers document the fast-paced recovery of tropical Hypolimnas bolina butterflies from the onslaught of a bacteria that killed only males.

For those who envision evolution creeping along only on glacial time scales, let this be a lesson.

A male Hypolimnas bolina, or blue moon butterfly
A male Hypolimnas bolina, or blue moon butterfly University of California at Berkeley

Researchers at the University of California at Berkeley and elsewhere have documented the super-swift recovery of tropical Hypolimnas bolina butterflies, also called blue moon or great eggfly butterflies, from the onslaught of a bacteria that killed only males. The bacteria had reduced the male population to about 1 percent of the overall species, but within 10 generations over less than a year in 2006, the males had recovered to 39 percent of the population, according to the researchers.

"To my knowledge, this is the fastest evolutionary change that has ever been observed," said Sylvain Charlat, lead author of a study of the phenomenon published Friday in the journal Science. Unlike mutations governing traits such as as wing color, a genetic change that affects the sex ratio of a population rapidly alters the species, he said.

The species live on the South Pacific island of Savaii, but male embryos were susceptible to bacteria called Wolbachia that's passed down from the butterfly mother.

Wolbachia and the blue moon butterfly illustrate what biologists call the Red Queen Principle, a term derived from the Lewis Carroll book Through the Looking-Glass in which Alice and the Red Queen run faster and faster but find they remain in the same place. In evolutionary terms, the concept applies to relationships between predators and prey or between hosts and parasites.

"In the case of H. bolina, we're witnessing an evolutionary arms race between the parasite and the host. This strengthens the view that parasites can be major drivers in evolution," Charlat said.

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