For the first time in the history of butterfly migration, a team of researchers mapped the epic 4,200 km (2610 miles) flight of the Painted Lady butterflies (Vanessa cardui) across the Atlantic Ocean.
“Covering the entire journey in 5 to 8 days from West Africa to French Guiana before arriving in South America, this unprecedented transatlantic journey opens new horizons in our current understanding of insect migration.”
In October 2013, Gerard Talavera, a researcher from the Botanical Institute of Barcelona at CSIC spotted these tattered-winged butterflies on the Atlantic beaches of French Guiana – a species not typically found in South America. This unusual sighting instigated an international study to investigate the origins and migration pattern of these butterflies.
Methods including wind trajectory reconstruction, genome sequencing, pollen DNA analysis, and isotope geolocation, were all a variety of cutting-edge techniques involved in this mapping.
In the beginning, the research team reconstructed wind trajectories for the period before the arrival of these butterflies in October 2013. This study led to the conclusion that a set of favorable wind conditions supported the transatlantic crossing from western Africa.
In the genetic studies (genome sequencing), it was revealed that these butterflies share a closer affinity to African and European populations, eliminating the possibility of North American origin. This was done by comparing its DNA to its populations worldwide.
Through pollen DNA analysis, the team identified two species of plants that these butterflies nectared on. They traced the flowers to be native to the Sahel region of Africa, thereby indicating the flight route across the Atlantic Ocean.
The isotope geolocation analysis pointed towards the potential natal origin in Western Europe (France, Ireland, the United Kingdom, or Portugal.) The researchers analyzed hydrogen and strontium isotopes in the butterflies’ wings, which act as chemical markers (fingerprints) to determine their natal origin.
Dr. Clément Bataille emphasizes the methodological novelty of the study: “It is the first time that this combination of molecular techniques including isotope geolocation and pollen metabarcoding is tested on migratory insects. The results are very promising and transferable to many other migratory insect species. The technique should fundamentally transform our understanding of insect migration.”
Another researcher, Roger Vila, comments, “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.”
The team of researchers led by Gerard Talavera from the Institut Botànic de Barcelona (IBB, CSIC-CMCNB), along with Tomasz Suchan from the W. Szafer Institute of Botany, and Clément Bataille, associate professor in the Department of Earth and Environmental Sciences at the University of Ottawa, helped in carrying out the research. This team also consisted of Megan Reich, a postdoctoral researcher from the Department of Biology at uOttawa, Roger Vila and Eric Toro Delgado, scientists from the Institute of Evolutionary Biology (IBE, CSIC-UPF), and Naomi Pierce, a professor of Biology in the Department of Organismic and Evolutionary Biology at Harvard University.
The researchers assessed the viability of this transatlantic flight by analyzing the energy expenditure for the journey. Sahara’s powerful air currents favored this non-stop 5 to 8 days of travel. As a result, the wind conditions proved advantageous for this migration to happen.
Eric Toro-Delgado, one of the co-authors of the article, explains, “The butterflies could only have completed this flight using a strategy alternating between active flight, which is costly energetically, and gliding 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.”
Earlier it was known that these Saharan wind currents could transport large amounts of dust from Africa to America, fertilizing the Amazon. This study resulted in the Saharan air layer being a significant aerial route for dispersion – even capable of transporting living organisms.
“The research indicates the existence of natural aerial corridors connecting continents and, potentially facilitating the dispersal of species on a much larger scale than what was previously imagined or known.”
Gerard Talavera, the study’s lead researcher, mentions, “Throughout history, migratory phenomena have been important in defining species distributions as we observe them today.”
The findings have been published in the journal Nature Communications.
As our climatic conditions continue to vary, researchers anticipate a potential increase in long-distance dispersal events, that would significantly impact biodiversity and ecosystems around the world.
Gerard Talavera, adds, “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.”
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