After the caterpillar gnaws the leaves of a plant of the bean family, it forms a chrysalis in which it develops into a butterfly. It’s an ordinary scene. It’s surprising to imagine that the same plant could be eaten by a dinosaur, or that the first species of bees that ever existed could fly around it. We’re talking about 100 million years ago, somewhere in presentday North and Central America.
“Defining this emergence date is important in order to link all aspects of butterfly evolution and draw a complete panorama,” Brazilian evolutionist Mariana Braga celebrates during her postdoctoral internship at the Swedish University of Agricultural Sciences in Uppsala. She took part in a study she describes as highly collaborative, involving a hundred researchers from 28 countries led by North American entomologist Akito Kawahara, curator of butterflies at the University of Florida’s Museum of Natural History in the United States . The work was published on Monday (May 15) in the journal Nature Ecology & Evolution.
To reconstruct this evolutionary history, global distribution, diversification and coevolution with host plants, The research group sequenced almost 400 genes from around 2,300 butterfly species. represent 92% of the genera already described and analyzed information on hundreds of publications. The result was compiled in a large publicly accessible database.
The extensive sequencing carried out as part of the project enabled the creation of a phylogeny or family tree of species that organizes the relationships between butterflies. A childhood dream came true for Kawahara. “When I was about 10 years old, my father took me to the American Museum of Natural History in New York, where we lived,” Pesquisa told FAPESP. As regular guests, father and son were granted the right to visit the visitorrestricted fifthfloor research area, a magical kingdom with narrow staircases and closets full of animals kept for study.
There he saw a tablet with a phylogenetic tree of butterflies full of question marks and dotted lines. “They were signs of what was not known,” he explains, intrigued by the idea of learning all about butterflies and filling in the gaps. “Now I’ve secured the funding for it.” The achievement also pays homage to the father who, before his death a few years ago, took the time to ask about his son’s research and discovered that he was in the process of discovering the origin of the discovering insects that populated his childhood.
timeline
A challenge in Kawahara’s work is obtaining data consistent with the phylogeny. Time estimation is mostly anchored in fossils, which are rare in butterflies the adults are delicate and the larvae very little firm. It was necessary to extract the possible information from only 11 fossils, and to support the data with extensive sequencing, robust statistical models, plenty of information from other studies, and geographic distributions from publications and entomological collections. Four supercomputers worked on it, three in the USA and one in Germany.
The results suggest that butterflies from an ancestor started to fly during the day and migrated across the Bering Strait to Asia and then spread south until they reached presentday India, which was then (75 to 60 million years ago) a paradise for Butterflies was island far from anywhere.
Southeast Asia became the largest center of butterfly diversity about 45 million years ago when they also spread to Africa. Over the past 30 million years, South and Central America has been the greatest center of biodiversity for these insects, where they have always existed and where species multiplied. “Butterflies need good habitats and plants, they follow resources, and we have a good idea of what they’ve been eating,” explains Kawahara. “Cold areas are not ideal.”
Some species have made relatively rapid strides in colonizing new areas in the geological time frame, while others have spent millions of years in the same place. The researcher explains that some butterflies have a great ability to migrate and manage to fly many kilometers over the sea, taking advantage of the journey on vegetation rafts or gusts of wind. Others who specialize in mountain tops are isolated in their areas. Some have long lives that allow them great voyages, others are ephemeral.
plant partnership
Essential to this occupation of the world was the widespread occurrence of legumes and grasses, the most common hosts. Braga explains that the association between butterfly species and plants that feed and house the developing larvae is quite specific.
The butterfly must find the exact plant to lay its eggs in, a coevolutionary relationship spanning millions of years. In order to draw inferences about the hosts of this long history, one must construct the most likely evolutionary models and rely on ample and wellcollected data. When two sister species use a host, it is likely that their ancestor also uses a host. And so, from mapping current features of phylogeny, it is possible to arrive at reasonable hypotheses about prehistoric habits.
During his PhD at Stockholm University, Sweden, Braga tested the theory that host diversity is important for the diversification and geographical distribution of these animals. To do this, he developed a method for analyzing a complete butterfly family including all host plant species. “This method is my calling card and that’s why Akito came to me in 2020 when I started working on this project.”
Nevertheless, the enormous amount of data did not seem to make it possible to carry out the analyzes in a timely manner. “The more than 1,300 species of butterflies for which we have data on host plants are related to 200 plant families,” he says. If the analysis worked, the amount of data would take months. But she has found a way to group plants that tend to be in relationships with butterflies, a method she described in a 2021 article published in the journal Ecology Letters. Arriving at 13 groups, it was possible to order the data.
Combining statistical analysis of the genetic data with information from more than 30,000 records of caterpillar use of host plants, the group found that twothirds of current butterfly species feed on a single plant family, while less than a third are generalists. and draws on two or more families. Anyone who has a preference for grasses and legumes tends to reject other alternatives. These plant families are found throughout the world and in all environments, and often lack strong chemical defenses against herbivores, allowing for intimate relationships that last millions of years.
“We’re getting to a point where we can be pretty sure about the age of the butterflies,” says biologist André Lucci Freitas of Campinas State University (Unicamp). In 2019, he took part in a study led by thenecologist Nicolas Chazot at Lund University in Sweden, which analyzed about ten stretches of DNA from nearly a thousand species of butterflies, alongside twelve fossils.
The results, published in the journal Systematic Biology, also point to an origin of around 100 million years ago. “With this large amount of data that’s available now, it’s possible to do other work,” he says.
It also celebrates the perception, reflected in butterfly diversity superiority, that South America is “amazing for biodiversity.” It is a continent with a large tropical area, whose environments are as diverse as the Amazon rainforest and the top of the Andes.
Kawahara is concerned about declining insect populations as a result of climate change. “Our work is important to understand how this happens.” Freitas reminds that this knowledge is essential for the preservation of the environment and the ecosystem services provided by the biomes, which ultimately affect the wellbeing of all organisms.