For the first time in the world, scientists map the 4,200 km transatlantic flight of the lady butterfly.

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

Using innovative multidisciplinary tools, a research team led by Gerard Talavera of the Institut Botànic de Barcelona, ​​Tomas Suchan of the W. Szafera Botanical Institute and Associate Professor Clément Bataille in the Department of Earth and Environmental Sciences at the University of Ottawa – with Megan Reich, a postdoctoral fellow in the Department of Biology in uOttawa, Roger Vila and Eric Toro Delgado, scientists from the Institute of Evolutionary Biology and Naomi Pierce, a professor of biology in the Department of Organic and Evolutionary Biology at Harvard University—set out on a scientific mission to trace the journey and origin of the mysterious Painted Ladies.

The butterfly migration was featured in an article entitled “Transoceanic flight over 4,200 km by painted butterflies”, published in The nature of communication on June 25, 2024.

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

After sequencing the genomes of these individuals and analyzing them in comparison to populations around the world, the researchers found that the butterflies are more closely related genetically to African and European populations. This result eliminated the possibility that these individuals came from North America, thus strengthening the hypothesis of an oceanic route.

The researchers used 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 only grow in tropical Africa, suggesting that the butterflies nectared on African flowers before making their transatlantic journey.

They analyzed isotopes of hydrogen and strontium in butterfly wings, a chemical signal that acts as a “fingerprint” of the region of natal origin. Combining isotopes with a habitat suitability model for larval growth revealed a potential natal origin in western Europe, possibly France, Ireland, the UK or Portugal.

Dr. Bataille says: “This is the first time that this combination of molecular techniques including isotopic geolocation and pollen metabarcoding has been tested on a migratory insect. The results are very promising and transferable to many other migratory insect species. This technique should fundamentally change our understanding of insect migration.”

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

Encouraged by the winds

The researchers assessed the viability of the transatlantic flight by analyzing the energy expenditure per trip. They predicted that a flight over the ocean lasting five to eight days without a stopover was feasible due to favorable wind conditions.

“The butterflies could only make this flight using a strategy of alternating between active flight, which is energy-intensive, and gliding downwind. We estimate that without the wind, the butterflies could only fly a maximum of 780 km before using up all their fat, hence their energy,” says Eric Toro-Delgado, one of the paper’s co-authors.

The Saharan air layer is highlighted by researchers as a significant airborne pathway for dispersal. These wind currents are known to carry large amounts of Saharan dust from Africa to the Americas and fertilize 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 finding suggests that there may be natural air corridors connecting continents that potentially facilitate species dispersal on a much larger scale than previously thought.

“I think this study shows well how much we tend to underestimate the dispersal abilities of insects. In addition, it’s entirely possible that we also underestimate the frequency of these types of dispersal and their impact on ecosystems,” says Megan. Reich, a postdoctoral fellow at the University of Ottawa who is also a co-author of the study.

Gerard Talavera, principal investigator of the study, adds: “Throughout history, migratory phenomena have been important in defining the distribution of species as we observe them today.”

The researchers point out that as a result of global warming and changing climate patterns, we may see more significant changes and a potential increase in long-range dispersal events. This could significantly affect biodiversity and ecosystems around the world.

“It is essential to promote systematic monitoring practices for the spread of insects that could help predict and mitigate potential risks to biodiversity resulting from global change,” concludes Gerard Talavera.