An international team of researchers have constructed a massive butterfly tree of life – and have used it to show that butterflies first evolved in North America.
Because of their delicate wings, butterflies don’t fossilise well, so there’s still a lot we don’t know about their origins.
Much of what we do know comes from examining the genetic diversity of the 19,000-odd species of butterfly alive today.
The research team, who have published their tree (or phylogeny) in Nature Ecology & Evolution, constructed a butterfly family tree based on the genetics of more than 2,300 species, representing 92% of all butterfly genera.
“This was a childhood dream of mine,” says lead author Professor Akito Kawahara, curator of lepidoptera (butterflies and moths) at the Florida Museum of Natural History, US.
“It’s something I’ve wanted to do since visiting the American Museum of Natural History when I was a kid and seeing a picture of a butterfly phylogeny taped to a curator’s door. It’s also the most difficult study I’ve ever been a part of, and it took a massive effort from people all over the world to complete.”
The researchers have poured all the butterfly information they collected into a publicly available database.
“In many cases, the information we needed existed in field guides that hadn’t been digitised and were written in various languages,” says Kawahara.
The phylogeny rests on 11 rare butterfly fossils, which were used to calibrate the family tree and help to establish how the various species of butterfly emerged.
From all of this data, the researchers believe they have a narrative for how butterflies spread across the world.
About 100 million years ago, the first butterflies started flying during the daytime and feeding on flowers, diverging from their moth cousins in central and western North America.
“The evolution of butterflies and flowering plants has been inexorably intertwined since the origin of the former, and the close relationship between them has resulted in remarkable diversification events in both lineages,” says co-author Professor Pamela Solitis, a curator at the Florida Museum.
The early butterflies crossed the (then) small strait to South America easily, and also radiated north to Russia and Asia, which were then connected to North America by land.
They spread quickly across Southeast Asia, the Middle East and the Horn of Africa.
More impressively, they also got to Australia and India, both then separated from Asia by big bodies of water. It’s possible they were also in Antarctica, while it was warmer and still connected to Australia.
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Despite these marine crossings happening quite early, it seems it took about 45 million years for butterflies to get over land to Europe. They still don’t have the genetic diversity in Europe that exists elsewhere in the world.
“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. Many butterflies in Europe are also found in Siberia and Asia, for example,” says Kawahara.
But most modern butterfly families had still been established by the time the dinosaurs were wiped out, 66 million years ago.