Newly created ‘tree of life’ shows butterflies came from America
(CN) — Scientists believe butterflies are roughly 100 million years old, having evolved from moths when dinosaurs still roamed the earth. And until recently, this evolutionary step, made possible by new nectar-rich flowers that also led to the development of bees, was thought to have first taken place in Southeast Asia.
But a new paper, published Monday in the journal Nature Ecology and Evolution, points to a different birthplace: North or Central America.
The work is the product of a collaboration between nearly 100 scientists all over the world, who collected DNA from more than 2,000 species of butterflies to build a sort of "evolutionary tree," a beautiful and complex diagram that describes the relationship between the roughly 19,000 different species of butterflies.
"Surprisingly, the relationships between butterflies was not very well known," said Akito Kawahara, the lead author of the paper and a professor and curator of Lepidoptera at the Florida Museum of Natural History. "In the past, we were not able to take DNA from old museum specimens. Now, because DNA sequencing technology has gotten significantly better in the last decade or so, we can do that efficiently."
Butterflies, with their paper-thin wings, are fragile creatures, and there are astonishingly few well-preserved butterfly fossils — only about 11 in the whole world. Those 11, though, proved crucial to the study.
The paper tells a remarkable story of how butterflies first appeared, in Central and North America, when the continents of the world looked completely different than they do today. Butterflies moved north, crossing into what is now Canada and then into Russia via the Bering Land Bridge, and then into Asia. From there, they spread to the Middle East and then the Horn of Africa. Eventually, the insects found the way into Australia — possibly via Antarctica, which was both warmer than and connected to Australia.
Finally, butterflies made it into Europe, after around 45 million years.
"Europe doesn’t have many butterfly species compared to other parts of the world, and the ones it does have can often be found elsewhere," Kawahara said. "Many butterflies in Europe are also found in Siberia and Asia, for example.”
For Kawahara, the butterfly tree is the culmination of a childhood dream. He grew up in both Japan and New York City, his artist father taking care to raise Kawahara in two different countries. When in the U.S., they would regularly visit the Natural History Museum. One weekend, when Kawahara was around 8 years old, they were given special access to the fifth floor research division, normally closed to the general public, where the museum kept its private collection — including countless metal drawers filled with butterfly specimens from all over the world.
"There was an office, and a scientist had poster on his door," Kawahara recalled. "It was a family tree of butterflies. There were question marks everywhere, and dotted lines. Nobody actually understood how butterflies were related. There was no DNA research at the time."
Kawahara and his team have been working since 2015, thank to a grant from the National Science Foundation. As part of their work, the created a publicly available database, having translated and transferred the contents of books, museum collections and even websites into a single digital repository.
"A lot of this information was found in field guides for a particular region, said Kawahara. "It was very hard to get global picture."
Many species of butterflies are thought to be shrinking in number, or at least moving to different parts of the world, presumably due to climate change.
"Having historical information on what they're feeding on and where they were located in the past is important," Kawahara said. "It’s changing, and we need to have that baseline."