In world first, researchers map 4,200km transatlantic flight of painted lady butterfly

In October 2013, Gérard Talavera, a researcher at the Barcelona Botanical Institute at CSIC, made a surprising discovery of painted lady butterflies on the Atlantic beaches of French Guiana, a species not generally found in South America . This unusual sighting prompted an international study to investigate the origin of these butterflies.

Using innovative multidisciplinary tools, the research team co-led by Gerard Talavera of the Botanical Institute of Barcelona, ​​Tomasz Suchan of the W. Szafer Institute of Botany and Clément Bataille, associate professor in the Department of Plant Sciences Earth and Environment from the University of Ottawa, with Megan Reich, postdoctoral researcher in the Department of Biology at the University of Ottawa, Roger Vila and Eric Toro Delgado, scientists from the Institute of Evolutionary Biology and Naomi Pierce , professor of biology in the Department of Organic and Evolutionary Biology at Harvard University, embarked on a scientific mission to trace the journey and origin of these mysterious painted ladies.

The butterfly migration was featured in the article “A transoceanic flight of more than 4,200 km by painted butterflies”, published in Natural communications on June 25, 2024.

First, the research team reconstructed wind trajectories for the period before these butterflies arrived in October 2013. They found exceptionally favorable wind conditions that could favor a transatlantic crossing from West Africa , opening the possibility that these individuals could have crossed the entire ocean. .

After sequencing the genomes of these individuals and analyzing them in comparison to populations around the world, the researchers discovered that the butterflies had a closer genetic relationship to African and European populations. This result eliminates the probability that these individuals came from North America, thus strengthening the hypothesis of an oceanic voyage.

The researchers exploited a unique combination of next-generation molecular techniques. They sequenced the DNA of the pollen grains carried by these butterflies. They identified two species of plants that grow only in tropical Africa, indicating that the butterflies were feeding on nectar from African flowers before embarking on their transatlantic journey.

They analyzed isotopes of hydrogen and strontium in the butterflies’ wings, a chemical signal that acts as a “fingerprint” of the region of natal origin. Combining the isotopes with a habitat model suitable for larval growth revealed a potential natal origin in Western Europe, possibly France, Ireland, the United Kingdom, or Portugal.

“This is the first time that this combination of molecular techniques, including isotope geolocalization and pollen metabarcoding, has been tested on migratory insects,” says Dr. Bataille. “The results are very promising and transferable to many other species of migratory insects. This technique is expected to fundamentally transform our understanding of insect migration. »

“We usually think of butterflies as symbols of the fragility of beauty, but science shows us that they can accomplish incredible feats. There is still much to discover about their abilities,” explains Roger Vila, researcher at the Institute of Evolutionary Biology (CSIC-Pompeu Fabra University) and co-author of the study.

Carried by the winds

The researchers assessed the viability of a transatlantic flight by analyzing the energy expenditure of the trip. They predicted that the flight over the ocean, lasting five to eight days nonstop, was feasible due to favorable wind conditions.

“The butterflies could only have achieved this flight by using a strategy alternating active flight, costly in energy, and gliding with the wind. We estimate that without wind, the butterflies could have traveled a maximum of 780 km before consuming all their fat and, therefore, their energy,” explains Eric Toro-Delgado, one of the co-authors of the article.

The Saharan air layer is highlighted by researchers as an important air route for dispersal. These wind currents are known to carry large quantities of Saharan dust from Africa to America, thereby fertilizing the Amazon. This study now shows that these air currents are capable of transporting living organisms.

The potential impact of migration in the context of global change

This discovery indicates that there may be natural air corridors connecting continents, potentially facilitating the dispersal of species on a much larger scale than previously imagined.

“I think this study demonstrates well how we tend to underestimate the dispersal abilities of insects. Additionally, it is entirely possible that we also underestimate the frequency of these types of dispersal events and their impact on ecosystems,” says Megan. Reich, postdoctoral researcher at the University of Ottawa and co-author of the study.

Gerard Talavera, lead researcher of the study, adds: “Throughout history, migratory phenomena have played an important role in defining the distribution of species as we observe them today.”

The researchers point out that due to global warming and climate change, we may see more notable changes and a potential increase in long-distance dispersal events. This could have a significant impact on biodiversity and ecosystems around the world.

“It is essential to promote systematic monitoring routines for dispersing insects, which could help predict and mitigate potential risks to biodiversity resulting from global change,” concludes Gérard Talavera.