Around 100 million years ago, an influential group of moths broke the norm by flying during the day instead of at night. This behavior shift allowed them to exploit nectar-rich flowers that had co-evolved with bees. This pivotal event eventually led to the evolution of all butterflies. In 2019, scientists confirmed the precise timing of this event through a comprehensive DNA analysis, debunking an earlier hypothesis that bats’ pressure prompted butterfly evolution after the extinction of dinosaurs.
Today, researchers have made further advancements in understanding the origins and dietary preferences of the first butterflies. To achieve this, scientists from numerous countries collaborated to construct the largest-ever butterfly tree of life, incorporating DNA samples from over 2,000 species representing all butterfly families and 92% of genera. Utilizing this framework, they unraveled the historical movements and feeding behaviors of butterflies, effectively solving a four-dimensional puzzle that pointed back to North and Central America. According to their findings, which were published in the journal Nature Ecology and Evolution on May 15, the first butterflies took flight in this region.
For Akito Kawahara, the lead author and curator of lepidoptera at the Florida Museum of Natural History, this research endeavor fulfilled a childhood dream. Reflecting on his inspiration, he mentioned visiting the American Museum of Natural History as a child and encountering a butterfly phylogeny picture adorning a curator’s door. However, he acknowledged the arduous nature of the study, describing it as the most challenging project he has ever been involved in. Completing it necessitated a tremendous collaborative effort from individuals worldwide.
With approximately 19,000 butterfly species in existence, piecing together the 100 million-year history of this group demanded comprehensive information about their present-day distributions and preferred host plants. Unfortunately, before this study, there was no centralized resource containing such data. Undeterred, the researchers decided to create their own publicly accessible database. They painstakingly translated and compiled information from books, museum collections, and disparate web pages into a unified digital repository. This allowed them to overcome language barriers and access crucial information.
The crucial backbone of this research rested on the discovery of 11 rare butterfly fossils. Given their delicate nature, butterflies are seldom preserved in the fossil record. However, these rare specimens provided invaluable calibration points for genetic trees, enabling researchers to determine the timing of significant evolutionary events.
The findings unveil a captivating narrative characterized by rapid diversifications, stumbling progress, and unlikely dispersals. Some butterfly groups embarked on incredible journeys across vast distances, while others remained relatively stationary even as continents, mountains, and rivers shifted around them.
The first appearance of butterflies can be traced to Central and western North America. During that time, North America was divided by a vast seaway, separating the continent. Meanwhile, present-day Mexico formed a continuous arc with the United States, Canada, and Russia. The joining of North and South America via the Isthmus of Panama had not yet occurred, but butterflies easily traversed the strait between the two landmasses.
Despite the proximity of South America to Africa, butterflies took a circuitous route, migrating into Asia via the Bering Land Bridge. Once in Asia, they rapidly spread across Southeast Asia, the Middle East, and the Horn of Africa. Remarkably, they even reached India, which was isolated as an island, surrounded by vast expanses of open sea.
The arrival of butterflies in Australia is particularly astonishing. During this period, Australia remained connected to Antarctica, the last remaining part of the supercontinent Pangaea. It is plausible that butterflies inhabited Antarctica when global temperatures were warmer, allowing them to migrate across the northern edge of the continent into Australia before the separation of the two landmasses.
In the northern regions of western Asia, butterflies resided on the outskirts for a possible duration of up to 45 million years before finally migrating into Europe. The reasons behind this prolonged pause remain unclear, but its impact is still evident today. As Kawahara explains, “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.”
Once butterflies established themselves, they rapidly diversified alongside their plant hosts. By the time dinosaurs became extinct 66 million years ago, nearly all modern butterfly families had emerged, with each family demonstrating a specific affinity for particular groups of plants.
Examining this association over an evolutionary timeline revealed that bean plants were the ancestral hosts for butterflies across various families. This was true not only for the ancestor of all butterflies but also within each family. Over time, bean plants expanded their range of pollinators to include various bees, flies, hummingbirds, and mammals, while butterflies expanded their feeding preferences. According to study co-author Pamela Soltis, the close relationship between butterflies and flowering plants has led to their remarkable diversification, transforming butterflies from a minor offshoot of moths into one of the largest groups of insects worldwide.
The intertwined evolution of butterflies and flowering plants has yielded extraordinary outcomes for both lineages, as stated by Pamela Soltis, a Florida Museum curator and distinguished professor.