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Two Butterfly Species Evolved Into Third, Study Finds

James Owen
for National Geographic News
June 14, 2006
 
A butterfly species from South America has been revealed as nature's
answer to Frankenstein's monster, scientists say.

New research shows the insect was originally created from two different butterflies in an evolutionary process many biologists didn't think possible.

The scientists arrived at this conclusion by successfully re-creating the butterfly in the lab, using "second-hand parts" from two related species.

Animals are thought usually to evolve in the opposite manner, when a single species gradually splits into two over many generations.

The team behind the discovery describes how it re-created the black, red, and yellow Heliconius heurippa butterfly in tomorrow's issue of the journal Nature.

Researchers say their creation reveals a process called hybrid speciation, in which the genes of two existing species combine to produce a third.

The study suggests hybridization may be more important to the evolution of new animals than had previously been thought.

Hybrids such as the mule, a cross between a donkey and a horse, are sterile. But the team says the butterfly hybrid brought together a combination of genes that allowed it to breed and there be considered a new species.

Evolution and Sex

Found in the high-altitude cloud forests of Venezuela and Colombia, H. heurippa was believed to be a hybrid because its wing patterns look like a mixture of two other Heliconius butterflies, scientists say.

(Learn about Colombian cloud-forest ecosystems.)

The insect has yellow markings from one species and red from the other, they explain.

DNA analysis of the butterfly revealed it to be genetically distinct from its two parent species, according to study co-author Chris Jiggins of the School of Biological Sciences at Scotland's University of Edinburgh.

The study also showed that the hybrid wing markings of H. heurippa play a key role in preventing the hybrid from attempting to mate with its parent species, the researchers explain.

In lab tests the team found that both the red and yellow wing markings were needed to attract mates and that when either color was removed experimentally from a female she wasn't attractive to males.

While the butterfly is able to breed with one of its parent species, "heurippa much prefers to breed with itself," Jiggins said.

"They are using this hybrid wing pattern for mate recognition—this is what keeps them different."

The butterfly has also isolated itself in other ways, he says.

The hybrid insect lives at a slightly higher altitude than its parent species, and in its juvenile caterpillar stage it appears to prefer different plants as food.

The butterfly is relatively new in evolutionary terms, Jiggins says, probably less than half a million years old.

While hybrid speciation is well documented in plants, the team says the new study is the first to recreate the process in the lab in an animal.

Fly Hybrid

Another recent study suggested that flies can likewise evolve through hybridization.

(Read "Evolution Revolution: Two Species Become One, Study Says.")

A team led by Dietmar Schwarz from Pennsylvania State University found that the Lonicera fly in the northeastern United States first developed as a cross of two existing fly species.

Schwarz says this type of evolution most likely occurs in animals where there are "lots of similar, fast-evolving species, such as in certain types of insects and fish."

Other evidence from Africa indicates that some cichlid fishes living in lakes first started off as hybrids.

Jiggins, co-author of the new study, says hybrid speciation is likely fairly common in closely related butterflies such as Heliconius.

"Probably the same thing has happened several times in that little group," he said.

Finding more examples could be difficult, however.

During the current study, Jiggins says, one of his South American colleagues was kidnapped by outlaws while hunting Heliconius butterflies in Colombia.

"He's fine," the researcher added, "but the area is a bit hectic."

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