In October 2013, a team of researchers, led by Gerard Talavera from the Botanical Institute of Barcelona (CSIC), made an unexpected discovery of Painted Lady butterflies on the Atlantic beaches of French Guiana in South America.
This sighting spurred an international study to investigate the origins and migration of these butterflies, employing a combination of cutting-edge techniques to solve the mystery. The research team, including experts from the Institut Botànic de Barcelona, the W. Szafer Institute of Botany, and the University of Ottawa, among others, reconstructed wind trajectories for the period preceding the butterflies' arrival.
They discovered favourable wind conditions that could support a transatlantic crossing from western Africa where these butterflies are usually found.
By sequencing the genomes of the butterflies and comparing them to global populations, researchers found a closer genetic relatedness to African and European populations. This finding suggested an oceanic journey, eliminating the possibility of a North American origin.
Further analysis using next-generation molecular techniques, including DNA sequencing of pollen grains carried by the butterflies and isotope analysis, indicated that the butterflies had nectared on African flowers before embarking on their journey.
Dr. Clément Bataille from the University of Ottawa highlighted the methodological novelty, stating: "It is the first time that this combination of molecular techniques including isotope geolocation and pollen metabarcoding is tested on migratory insects."
The researchers assessed the viability of a transatlantic flight by analysing energy expenditure. They concluded that the butterflies could have completed the flight using a strategy of alternating between active flight and gliding on the wind.
Without wind assistance, the butterflies could have flown a maximum of 780 km before depleting their energy reserves.
"The butterflies could only have completed this flight using a strategy alternating between active flight and gliding on the wind," explained Eric Toro-Delgado, a co-author of the study.
The study also highlighted the role of the Saharan air layer as a significant aerial route for dispersion. These wind currents, known for transporting Saharan dust to America, were shown to be capable of carrying living organisms.
Megan Reich, a Postdoctoral Fellow at the University of Ottawa, commented: "I think this study does a good job of demonstrating how much we tend to underestimate the dispersal abilities of insects."
The researchers noted that global warming and changing climate patterns might increase long-distance dispersal events, impacting biodiversity and ecosystems worldwide.
Lead researcher Gerard Talavera emphasised the importance of systematic monitoring of dispersing insects to predict and mitigate potential risks to biodiversity resulting from global change.
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