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Scientists Flutter Over Amazing Speed of Evolution in Butterflies

By Chris Hogg     Jul 13, 2007 in Science
Natural selection takes hundreds or thousands of years, so when scientists found a South Pacific island butterfly that evolved in only 10 generations, they were amazed. Scientists say it is the fastest example of natural selection ever observed.
Digital Journal — With the looming danger of a deadly parasite, Hypolimnas bolina butterflies (also known as Blue Moon or Great Eggfly butterflies) on the Samoan islands of Savaii and Upolu (islands in the Pacific) evolved with incredible speed.
A study team from the University College London have been observing the butterflies, saying the population of males dropped to a dangerous 1 per cent after a parasite began targeting males. The Wolbachia bacteria is a parasite that gets passed down through the female, killing off males before they can hatch. But in a span of 10 generations, the males formed genetic defences to the parasite, allowing the population to grow by almost 40 per cent in less than one year.
Gregory Hurts, a member of the team, told MSNBC, “We usually think of natural selection as acting slowly, over hundreds or thousands of years. But the example in this study happened in a blink of the eye, in terms of evolutionary time."
Researchers say this case is "the fastest example of natural selection observed to date," indicating evolution can happen incredibly fast when the risks are high.
Their results are published in the journal Science.
The challenge for scientists was trying to determine if the males were dying because of genetic changes in themselves or in the parasite. To figure it out, they bred infected female butterflies with those from a different island that had no genetic mutation. The offspring was then bred with butterflies from an island that did not have the parasite in an effort to dilute the gene, and it resulted in total male killing (which researchers say is due to suppression and not any other phenomenon).
The speedy recovery and re-population of the male butterfly population showed scientists that rapid natural selection helps a species survive. Typically a slow process, natural selection can move very quickly when a population is exposed to severe risk of extinction.
"It is the speed of the process that demonstrates the intensity of the selection," researcher, Sylvain Charlat, told Reuters. "The take-home message is that evolution can be really, really fast."
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