Mapping the 4,200 km transatlantic flight of the Painted Lady butterfly

In October 2013, Gerard 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 usually found in South America. This unusual observation prompted an international study to investigate the origin of these butterflies.

A combination of new techniques solves the riddle

Using innovative multidisciplinary tools, the research team co-led by Gerard Talavera of the Institut Botànic de Barcelona (IBB, CSIC-CMCNB), Tomasz Suchan of the W. Szafer Botanical Institute and Clément Bataille , associate professor in the Department of Earth and Environmental Sciences at 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 at the Institute for Evolutionary Biology (IBE, CSIC-UPF) and Naomi Pierce, professor of biology in the Department of Organizational and Evolutionary Biology at Harvard University – embarked on a scientific mission to trace the journey and origin of these mysterious Painted Ladies.

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

After sequencing the genomes of these individuals and analyzing them against populations around the world, the researchers found that the butterflies were more closely related to African and European populations. This result eliminates the likelihood that these individuals came from North America, strengthening the hypothesis of an ocean 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.

Dr. Bataille emphasizes the methodological novelty of this study: “This is the first time that this combination of molecular techniques including isotopic geolocation and pollen metabarcoding has been tested on migratory insects. The results are very promising and transferable to many other species of migratory insects. The technique should fundamentally transform 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 capabilities,” says 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 journey. They predicted that the flight over the ocean, lasting 5 to 8 days non-stop, was feasible due to favorable wind conditions. “The butterflies could only have achieved this flight by using a strategy alternating between active flight, which is energetically costly, and gliding flight with the wind. We estimate that without wind, the butterflies could have flown a maximum of 780 km before consuming all their fat and therefore their energy,” comments 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 natural air corridors connecting continents may exist, potentially facilitating the dispersal of species on a much larger scale than previously imagined.

“I think this study really shows how much we tend to underestimate the dispersal abilities of insects. And it’s quite possible that we also underestimate the frequency of these types of dispersal events and their impact on ecosystems,” says Megan Reich, a 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 changing weather patterns, we could see more marked changes and a potential increase in long-distance dispersal events. This could have significant impacts 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 Gerard Talavera.

A NEWSPAPER ARTICLE :
Tomasz Suchan, Clément P. Bataille, Megan S. Reich, Eric Toro-Delgado, Roger Vila, Naomi E. Pierce, Gerard Talavera. A transoceanic flight of more than 4,200 km of beautiful lady butterflies. Natural communications2024; 15 (1) DOI: 10.1038/s41467-024-49079-2