Scientists recreate evolution of butterfly species

A species of butterfly has been recreated in the laboratory in an experiment that may have captured the real evolutionary steps leading to the formation of a new breed of animal.

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 from South America - first came about as a distinct entity 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 in Panama City. The study, published inNature, sheds fresh light on how species come into existence. It also shows that the process can occur very quickly when two closely related species are occasionally able to interbreed to produce fertile hybrids.

There are about 60 species of butterfly belonging to the Heliconius genus and all have distinctive matt-black wings with red, orange, yellow and white markings to indicate to 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 set up a laboratory breeding programme and found thatH. heurippa could be quickly recreated by interbreeding these two parental types.

"We found a wing pattern almost identical to that of the hybrid can be obtained in months - just three generations of lab crosses," said Mauricio Linares, of the University of the Andes in Colombia. "Natural hybrids from San Cristobel in Venezuela show wing patterns very similar to H. heurippa, further supporting the idea of a hybrid origin of this species."

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

Chris Jiggins of the University of Edinburgh said this may be related to the wing patterns in a group of butterflies that are important in warning away predators. Wing coloration is so finely tuned that even slight deviations in colours or patterns produce confusing signals that could result in greater predation.

"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 shun... their parental species," he said.