The research was carried out by an international team of scientists led by the Spanish National Research Council (Consejo Superior de Investigaciones Científicas, CSIC). The study involved researchers from the Botanical Institute of Barcelona (IBB), a joint centre of CSIC and the Museum of Natural Sciences in Barcelona, the Institute of Evolutionary Biology (IBE, CSIC-Universitat Pompeu Fabra) as well as from the W. Szafer Institute of Botany of the Polish Academy of Sciences in Kraków, the University of Ottawa (Canada) and Harvard University (USA).

The researchers documented a transoceanic flight of more than 4,200 km from West Africa to French Guiana in South America by painted lady butterflies (Vanessa cardui), setting a record for an insect.

In October 2013, Gerard Talavera, a CSIC researcher at the Botanical Institute of Barcelona, identified several female painted lady butterflies on the Atlantic beaches of French Guiana. This was unusual, as this species is not found in South America.

Scientists initially assumed that the butterflies could have originated in North America, where the nearest populations are found, or that they travelled from Africa or Europe. By analysing wind trajectories, researchers observed a sustained directional pattern from West Africa, opening the possibility that the butterflies had crossed the Atlantic

Studying the genetic diversity of the butterflies required collecting samples from populations on all continents. The researchers determined that the specimens observed in South America were related to populations in Europe and Africa, ruling out the possibility of a North American origin.

The researchers also analysed the pollen DNA on the bodies of butterflies. They identified two plant species found only in tropical Africa, proving that the butterflies visited flowers in that region.

They also analysed the stable isotopes of hydrogen and strontium from the butterflies' wings. The wings preserve isotopic signatures unique to the place where the insect fed in its larval stage. Based on these data, the researchers determined that the butterflies most likely originated from western European countries such as France, Ireland, the United Kingdom or Portugal.

'The painted lady butterflies reached South America from West Africa, flying at least 4,200 km over the Atlantic. But their journey could have been even longer, starting in Europe and passing through three continents, implying a migration of 7,000 km or more. This is an extraordinary feat for such a small insect', says Clément Bataille, a professor at the University of Ottawa in Canada and the study co-author.

'We tend to see butterflies as a symbol 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, a researcher at the Institute of Evolutionary Biology (IBE, CSIC-Universitat Pompeu Fabra) and co-author of the study.

The researchers have modelled the energetic cost of the journey and calculated that the flight across the ocean, without any stop, lasted between five and eight days. This was energetically possible because it was facilitated by favourable wind.

'The butterflies could only have completed this flight using a strategy alternating between minimal effort to avoid falling into the sea, facilitated by ascending winds, and active flight, which requires more energy consumption. We estimate that without wind, the butterflies could have flown a maximum of 780 km before exhausting all their fat and thus their energy', says Eric Toro-Delgado, one of the authors of the paper.

The researchers emphasise the importance of winds from the Sahara, which are prevalent throughout the year, transport large amounts of Saharan dust from Africa to America and participate in important biogeochemical cycles. Evidently, living organisms can also be transported this way.

The discovery suggests that natural aerial corridors connecting continents may exist, facilitating the dispersal of species on a much larger scale than previously thought.

'This discovery opens new perspectives on the capabilities of insects to disperse over long distances, even across seas and oceans. It is possible that we are underestimating the frequency and impact of these movements on our ecosystems', says Gerard Talavera, leader of the study. 'Throughout history, migratory phenomena have been important in defining the distributions of species that we observe today', he adds.

The researchers emphasize that with global warming and changing climatic patterns, we will likely observe greater changes and even an increase in these long-distance dispersal events, which could have significant implications for biodiversity and ecosystems worldwide. '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', says Talavera. (PAP)

Paweł Wernicki

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tr. RL