A group of butterflies fly across the Atlantic Ocean

Scientists have documented a flight of more than 4,200 kilometres over the Atlantic Ocean from Africa to French Guiana by carder butterflies (of the Vanessa cardui species). It is the first time that a group of butterflies has been scientifically proven to fly across the Atlantic Ocean. The distance covered is a record for an insect.

The study was carried out by an international team made up of experts from the Barcelona Botanical Institute (IBB, joint center of the Natural Sciences Museum Consortium of Barcelona and the Higher Council for Scientific Research (CSIC) in Spain), as well as the Institute of Evolutionary Biology ( IBE, joint center of the CSIC and the Pompeu Fabra University in Barcelona), the W. Szafer Botanical Institute (Poland), the University of Ottawa (Canada), and Harvard University (United States).

The trip lasted between five and eight days and was energetically possible thanks to the help of the trade winds.

In October 2013, researcher at the Barcelona Botanical Institute of the CSIC Gerard Talavera identified several cardera butterflies on the Atlantic beaches of French Guyana. These observations were completely unusual, since this species is not found in South America. Where they came from?

A multidisciplinary approach has allowed us to decipher the route and origin of these butterflies. The two starting hypotheses were that they could have been born in North America, where the closest populations are found, or in Africa or Europe. By analyzing wind trajectories, the researchers observed a sustained pattern of directionality from west Africa, which raised the possibility that they had crossed the Atlantic.

By studying the genetic diversity of butterflies, which required collecting samples from populations from all continents, the researchers determined that the specimens observed in South America were related to populations in Europe and Africa, which in turn ruled out the possibility of an origin in North America. The researchers also analyzed the DNA of the pollen that the butterflies carried on their bodies, and identified two species of plants that are only found in tropical Africa, demonstrating that the butterflies visited flowers in that region.

Finally, the team, led by Tomasz Suchan from the W. Szafer Botanical Institute, analysed stable isotopes of hydrogen and strontium from the butterflies’ wings. The wings preserve isotopic signatures characteristic of the place where they were raised in their larval phase, which allows them to infer their natal origin. With this data, they determined that their origin was most likely in Western European countries such as France, Ireland, the United Kingdom or Portugal.

“The cardinal butterflies arrived in South America from West Africa, flying at least 4,200 kilometers over the Atlantic. But their journey could have been even longer, starting in Europe and passing through three continents, which represents a migration of 7,000 kilometers or more. This is an extraordinary milestone for such a small insect,” explains Clément Bataille, professor at the University of Ottawa in Canada and co-author of the study.

“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, researcher at the Institute of Evolutionary Biology and co-author of the study.

A cardigan butterfly about to take flight. (Photo: Roger Vila)

With the help of the winds

The researchers have modelled the energetic cost of the journey and calculate that the flight across the ocean, without any stops, lasted between 5 and 8 days. This was energetically possible because it was facilitated by favourable wind currents. “The butterflies could only have completed this flight using a strategy that alternated between minimal effort to avoid falling into the sea, facilitated by upwelling winds, and active flight, which requires greater energy expenditure. We calculate that, without wind, the butterflies could have flown a maximum of 780 kilometres until they had consumed all their fat and, therefore, their energy,” says Eric Toro-Delgado, one of the authors of the study.

The researchers highlight the importance of the Saharan air layer as a potential aerial dispersion highway. These wind currents, which are predominant throughout the year, transport large quantities of Saharan dust from Africa to America and participate in important biogeochemical cycles. The portion of transported biological components, including living organisms, however, should be studied in depth.

Migrations in the context of global change

This finding indicates that there may be natural air corridors that connect continents and that they could be facilitating the dispersal of species on a much larger scale than previously imagined. “This discovery opens new perspectives on the abilities of insects to disperse over long distances, even across seas and oceans. It is possible that we are underestimating the frequency and impact that these movements have on our ecosystems,” says Gerard Talavera. “Throughout history, migratory phenomena have been important in defining the distributions of species as we see them today,” he adds.

The researchers highlight that, with global warming and changes in climate patterns, it will be likely to observe greater alterations and even an increase in these long-distance dispersal events, which could have important repercussions for biodiversity and ecosystems throughout the world. world.

“It is essential to promote systematic monitoring routines of dispersing insects, which could contribute to predicting and mitigating possible risks to biodiversity derived from global change,” concludes Talavera.

The study is titled “A trans-oceanic flight of over 4,200 km by painted lady butterflies”. It has been published in the academic journal Nature Communications. (Source: IBB / CSIC)