Butterfly effect

Scientists have retraced the evolutionary steps that may have given rise to a hybrid butterfly species, in the laboratory Steve Connor

A species of butterfly has been retraced in the laboratory during a remarkable experiment. The experimental species was produced from two different types of butterfly that had been interbred to produce a fertile hybrid, which was shown in subsequent tests to prefer mating with its own kind.

British and American researchers said that this is probably how the brightly coloured Heliconius heurippa—a wild species found in South America— first came about as a distinct entity many thousands of years ago.

"We recreated the evolutionary steps that may have given rise to Heliconius heurippa, a hybrid butterfly species, in the lab," said Jesus Mavarez of the Smithsonian Tropical Research Institute, based in Panama City.

The study, published in the journal Nature, sheds fresh light on how new species come into existence. It also shows that the process can occur almost overnight when two closely related species are occasionally able to interbreed to produce fertile hybrids.

There are about 60 different species of butterfly belonging to the Heliconius genus and all have distinctive matt-black wings with colourful red, orange, yellow and white markings to indicate to potential predators that the butterflies are poisonous to eat.

Scientists had long suspected that the H. heurippa, which has red and yellow stripes on its wings, was closely related to two similar looking butterflies, H. cydno and H. melpomene. They therefore set up a laboratory breeding programme and found that the H. heurippa species could be quickly recreated by interbreeding these two parental types.

The key finding from the experiment was that the hybrid offspring preferred to mate among themselves rather than breeding with butterflies belonging to either of their parental types.

"Butterflies tend to choose partners that look like themselves, as they are attracted to others with wing patterns similar to their own," Dr Jiggins said.

"So, once the new pattern was established, these individuals have tended to mate with one another and shunned their parental species," he said.

The scientists conducted a series of experiments showing that when they covered the red or the yellow stripes on models of H. heurippa females, the males took no interest in mating with them.

"The study shows that all the hybrid elements of the pattern are necessary for mating, and hence play a role in keeping H. heurippa as a species distinct from its parents," he said.

—By arrangement with The Independent