Whether swallowtail, admiral or small tortoiseshell: nature has produced a large variety of butterflies. But when and where these diurnal, colorful butterflies originated was previously unclear. Now the first comprehensive genetic and geographic family tree of butterflies provides the answer. Accordingly, the ancestor of all butterflies developed around 100 million years ago in western North or Central America. From there, the butterflies spread across the world and were the last to reach Europe. The first forage plants of the ancient butterflies were probably early representatives of legumes, as the reconstruction suggests.
They are among the stars of the insect world: the beauty and diversity of butterflies has fascinated naturalists, scientists and laypeople for centuries. No wonder, then, that the lifestyle, adaptations, and interrelationship of butterflies, their food plants, and their predators are among the best studied in the insect kingdom. Nevertheless, the evolutionary background of butterflies remained incomplete. It seems clear that the first ancestors of today's butterflies converted their biting mouth parts into suction proboscis around 200 million years ago. However, these first butterflies more closely resembled modern-day moths and were nocturnal. It was previously unclear when the first butterflies emerged from these primordial moths.
Cradle stood in North America
To answer this question, Akito Kawahara from the Florida Museum of Natural History in Gainesville and his team have now genetically and geographically reconstructed the evolution of butterflies. To do this, they collected and analyzed DNA samples and descriptions of 2,300 butterfly species from 90 countries. Eleven fossil butterflies were also included in the analyses. By comparing 391 genes in all species, the biologists were able to understand the evolutionary development of the butterflies and create a new family tree for this group of butterflies. It shows when and where which butterfly groups developed and spread. The team was also able to determine when the first ancestor of all butterflies arose: "The butterflies arose around 101 million years ago from nocturnal, herbivorous moths," report Kawahara and his colleagues.
The reconstruction also provides clues as to where this first butterfly lived: “The range evolution models consistently suggest that the butterflies originated in the Americas. Their origin lies in the area that today includes western North America or Central America,” the scientists report. At that time, around 100 million years ago, the North American continent was still divided into eastern and western halves by a large inland sea. The butterflies originated in the western half. From there, the diurnal butterflies initially spread across the neotropics in the millions of years that followed. “From around 60 million years ago, this region was an important bioregion for the formation of new butterfly species. Many new lineages then spread from this area to other regions,” say the researchers. The butterflies first reached Asia via the Beringia land bridge, then the Middle East and Africa. Even India, Australia and Antarctica have been colonized by butterflies despite their isolated location.
Europe as a latecomer, legumes as fodder
Europe, on the other hand, remained free of butterflies for a long time: the spread of butterflies stalled in western Asia for around 45 million years, as the team explains. However, it is still unknown why the butterflies did not advance further west at that time. Only around 17 million years ago did the first two butterfly lines venture into Europe, including the ancestors of the subfamily that includes species such as the peacock butterfly, painted lady, small tortoiseshell, maple leaf or admiral. The consequences of this late butterfly colonization can still be seen in Europe today: "Compared to other parts of the world, Europe has relatively few butterfly species," says Kawahara. “And the species that are found in Europe are often found elsewhere. Many European butterflies are also found in Siberia and Asia.”
The researchers were also able to reconstruct which food plants the larvae of the primeval butterflies probably preferred. This is possible because most butterfly species use a narrow range of host plants and show corresponding genetic adaptations. "We looked at these associations across the evolutionary timeline, and legumes emerged as the original host plants in almost every butterfly family," reports Kawahara. The ancestor of all butterflies could have fed on the ancestor of all legumes as a larva. Because the oldest common ancestor of all beans, peas, lentils, soybeans or peanut plants originated around 100 million years ago. "The evolution of butterflies and flowering plants has been inextricably linked since the emergence of butterflies," says co-author Pamela Soltis of the Florida Museum of Natural History. "
Source: Akito Kawahara (Florida Museum of Natural History, Gainesville) et al., Nature Ecology & Evolution, doi: 10.1038/s41559-023-02041-9