About 100 million years ago, a group of pioneer moths began flying during the day instead of at night, taking advantage of the nectar-rich flowers that co-evolved with bees. This single event led to the evolution of all butterflies.
Scientists have known the exact timing of this event since 2019, when a large-scale analysis of DNA ruled out an earlier hypothesis that pressure from bats drove the evolution of butterflies after the extinction of the dinosaurs.
Now, scientists have discovered where the first butterflies originated from and the plants they depended on for food.
Before reaching these conclusions, researchers from dozens of countries had to create the world’s largest butterfly tree, compiled with DNA from more than 2,000 species representing all butterfly families and 92% of genera. Using this framework as a guide, they trace the butterflies’ movements and their feeding habits through time in a four-dimensional puzzle that led to North and Central America. According to their findings, published Monday in the journal Ecology and evolutionThis is where the first butterflies flew.
For lead author Akito Kawahara, curator of Lepidoptera at the Florida Museum of Natural History, the project was a long time coming.
“This was my childhood dream,” he said. “It’s something I’ve wanted to do since visiting the American Museum of Natural History as a child and seeing a picture of a butterfly’s genus taped to a curator’s door. It’s also the hardest study I’ve ever been involved in, and it took an enormous effort of people all over the world to complete it.”
There are about 19,000 species of butterflies, and piecing together the group’s 100 million-year history requires information about their modern distributions and host plants. Prior to this study, there was no single place researchers could go to access this type of data.
“In many cases, the information we needed was in field guides that were not digitized and written in different languages,” Kawhara said.
Undeterred, the authors decided to create their own publicly available database, translating and transferring the contents of orphaned books, museum collections, and web pages into a single digital repository.
Underlying all of this data were 11 rare butterfly fossils, without which the analysis would not have been possible. Butterflies are rarely preserved in the fossil record with paper-thin wings and threadlike hairs. The few that can be used as calibration points on genetic trees, allowing researchers to record the timing of key evolutionary events.
The results tell a dynamic story–one filled with rapid variations, faltering progression, and improbable distractions. Some groups traveled impossibly vast distances while others seemed to stay in one place, standing still as continents, mountains, and rivers moved around.
Butterflies first appeared somewhere in central and western North America. At that time, North America was divided by a wide sea passage that cut the continent in two, while present-day Mexico joined in a long arc with the United States, Canada and Russia. North and South America have not yet joined across the Isthmus of Panama, but the butterflies had little difficulty crossing the strait between them.
Despite the relatively close proximity of South America to Africa, butterflies have come a long way, migrating to Asia through the Bering Land Bridge. From there, they quickly covered the ground, spreading to Southeast Asia, the Middle East, and the Horn of Africa. They even reached India, which was then a lonely island, separated on all sides by miles of open sea.
Even more astonishing is their arrival in Australia, which remains sewn to Antarctica, the last combined remnant of the supercontinent Pangea. The butterflies likely lived in Antarctica when global temperatures were warmer, making their way across the northern edge of the continent to Australia before the two landmasses separated.
Farther north, butterflies stayed on the edge of western Asia for up to 45 million years before finally migrating to Europe. Kawhara explained that the reason for this extended stop is not clear, but its effects are still evident today.
“Europe does not have as many species of butterflies as compared to other parts of the world, and species found elsewhere can be found. Many butterflies are also found in Europe in Siberia and Asia, for example.”
Once established, butterflies quickly diversify along with their plant hosts. By the time the dinosaurs were wiped out 66 million years ago, nearly all of the modern butterfly families had arrived on the scene, each one seeming to have a particular affinity for a particular group of plants.
“We looked at this association over an evolutionary time scale, and in almost every family of butterflies, bean plants appeared to be the ancestral hosts,” Kuhara said. “This was true of the ancestors of all butterflies, too.”
Since then bean plants have increased their pollinator list to include many bees, flies, hummingbirds, and mammals, while butterflies have similarly expanded their palate. According to study co-author Pamela Soltis, Florida Museum Curator and Distinguished Professor, the plant partnerships forged by the butterflies helped transform them from a small breed of moths into what today is one of the largest insect populations in the world.
“The evolution of butterflies and flowering plants has been inexorably intertwined since the genesis of the former, and their close relationship has led to remarkable diversification events in both lineages,” she said.