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In study, two species become one

June 14, 2006
Courtesy Nature
and World Science staff

Researchers say they have interbred two butterfly species to create a third. It’s the first clear evidence that two animal species can evolve to form one, they add, rather than the usual case in which one species branches into two.

A natural hybrid between H. cydno and H. melpomene, from San Cristobal, Venezuela. (© Mauricio Linares, Universidad de Los Andes)

The sci­en­tists in­ter­bred He­li­co­nius cydno, which is black with white and yel­low marks, with H. mel­pom­e­ne, which is black with red, yel­low and or­ange marks. 

The out­come was H. heurippa, an­oth­er spe­cies, they found. A mix of the first two in both its ge­nome and wing pat­tern, H. heurippa al­so oc­curs nat­u­ral­ly.

Cre­a­tion of new spe­cies through in­ter­breed­ing of two oth­ers, called hy­brid spe­ci­a­tion, is com­mon among plants. 

But it was thought to be rare or ab­sent in an­i­mals. For them, sci­en­tists be­lieved hy­brid off­spring would be less like­ly to sur­vive and breed than the par­ent spe­cies. Some hy­brid an­i­mals ex­ist, but they usu­al­ly are ster­ile.

For hybrid speciation to work, the hybrids must be not only fertile but also “reproductively isolated,” the researchers said. This means that for whatever reason, they wouldn’t breed again in large numbers with the parent species. Otherwise they themselves would disappear as a distinct group.

The researchers said they showed the isolation occurs in this case. They gave the new butterflies a chance to mate with either their parent species or other H. heurippa individuals. The insects were far more likely to mate with their own kind, the scientists reported.

The study, by Jesús Mavárez of the Smithsonian Tropical Research Institute in Panama and Mauricio Linares of the Universidad de los Andes in Bogota, Colombia, is detailed in the June 15 issue of the research journal Nature.

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The scientists interbred Heliconius cydno, which is black with white and yellow marks, with H. melpomene, which is black with red, yellow and orange marks. 

The outcome was H. heurippa, another species, they found. A mix of the first two in both its genome and wing pattern, H. heurippa also occurs naturally.

Creation of new species through interbreeding of two others, called hybrid speciation, is common among plants. 

But it was thought to be rare or absent in animals. For them, scientists believed hybrid offspring would be less likely to survive and breed than the parent species. Some hybrid animals exist, but they usually are sterile.