Giving hybrids some respect

Jon Chase/Harvard Staff Photographer

Marcus Kronforst (left) and Krushnamegh Kunte at Harvard’s FAS Center for Systems Biology used genetic analysis to examine the evolutionary history of the Appalachian tiger swallowtail, discovered in 2002. “Our work provides perhaps the first animal example that illustrates how hybrid species may be selectively favored when they inherit from their parent species-specific combinations of genes that underlie important ecological traits,” said Kunte, a postdoctoral fellow at the center.

Kunte et. al. recently discovered that the Appalachian tiger swallowtail butterfly evolved through the hybridization of Eastern and Canadian swallowtails. It is a rare example of hybrid speciation in an animal. Pictured here is a female Appalachian tiger swallowtail. Credit: Krushnamegh Kunte.

Harvard researchers are bringing new respectability to hybrids, showing that not all are evolutionary dead ends or short-lived mistakes and that some not only encompass the best traits of both parents, but create a unique mix that can endure as a separate species.

Researchers at Harvard’s FAS Center for Systems Biology used genetic analysis to examine the evolutionary history of a recently recognized species of butterfly, the Appalachian tiger swallowtail, discovered in 2002. The Harvard analysis confirmed what other researchers had suspected, that the butterfly was a hybrid of the Canadian tiger swallowtail and the more southern eastern tiger swallowtail. Further, the researchers showed that the hybrid species originated when males from the Canadian species mated with females from the south.

“Our work provides perhaps the first animal example that illustrates how hybrid species may be selectively favored when they inherit from their parent species-specific combinations of genes that underlie important ecological traits,” said Krushnamegh Kunte, a postdoctoral fellow at the center and lead author of the study, which was published online Sept. 8 in PLoS Genetics.

The research shows that the species formed in a burst of hybridization that likely occurred during the last interglacial period. As the range of the cold-adapted Canadian tiger swallowtail retreated north with the glaciers, the range of the warm climate-adapted eastern tiger swallowtail advanced northward and up into the Appalachian Mountains. The two species subsequently intermingled in the mountains during a changing climate.

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