Painted lady butterflies are remarkable travelers. The ones we spot in Europe migrate from Africa to Sweden, eventually returning to regions north and south of the Sahara. But what factors determine why some butterflies undertake lengthy journeys while others do not? Researchers, including those from the Institute of Science and Technology Austria (ISTA), have found that various migration patterns are influenced by environmental conditions instead of being hardwired in the butterfly’s genetics.
On a warm June day, a team of scientists donned in sun hats and armed with nets are trekking along a trail in the Catalan mountains. They are on the lookout for painted ladies—vibrant orange butterflies adorned with a delicate black-and-white pattern. Capturing these butterflies proves challenging as they are strong and persistent flyers, a realization that evolutionary biologist Daria Shipilina has come to accept.
Having previously studied plants and birds, Shipilina makes an attempt to catch one of these captivating butterflies in flight. Her net sways wildly without success. Finally, a few butterflies pause for some nectar, providing her with the long-awaited opportunity. With a swift movement, she captures one. This triumph is significant for the biologist and highlights the tenacity and vigor of these astonishing butterflies.
Every year, painted ladies embark on an impressive migratory route from Northwest Africa to Sweden, always in search of optimal environmental conditions that support their survival and reproduction. A collective of scientists, along with citizen science initiatives, has been working to decipher the migratory routes of these butterflies. A recent multidisciplinary study sheds new light on their behaviors. Notable contributors include Shipilina—formerly with the University of Uppsala and currently a postdoc in Nicholas Barton’s group at ISTA—who collaborated with several institutions such as the University of Ottawa, CSIC-CMCNB in Barcelona, SOS Savane, the Polytechnic Higher School of Dakar, and the Technical University of Darmstadt. Their findings are published in PNAS Nexus.
No distance too far, no burden too heavy
“The painted lady is exceptionally stunning and colorful,” shares Shipilina. “Witnessing them gather in large groups is truly a sight to behold. However, what makes them unique is their extraordinary long-distance migrations.”
These butterflies undertake a remarkable 10,000 km round trip between Africa and Europe each year. They accomplish this through successive generations that seek ideal breeding conditions for their young. “Each butterfly contributes to one part of the annual migration, with their offspring carrying on the journey,” explains Shipilina.
The vibrant insects initiate their epic journey during spring, departing from Northwest Africa and flying over the Mediterranean Sea into Europe. Other generations then continue to Great Britain, even reaching Sweden’s Arctic tundra for summer.
Previously, it was thought that butterflies would die in Sweden due to the cold weather that follows summer. However, research reveals that painted ladies return to warmer areas in the fall, confirming a cyclical migration pattern. While some remain in the Mediterranean, others journey back to Africa, often crossing the Sahara. But how do they navigate this route? Do they possess distinct navigational tools?
Where have you been, where are you headed?
To explore this question, Shipilina and her colleagues traveled to gather painted ladies from regions both north and south of the Sahara, including Benin, Senegal, Morocco, Spain, Portugal, and Malta.
They employed isotope geolocation to determine the geographic origins of each butterfly. “The fundamental principle of this method is that the isotopic composition — the stable isotopes — in the wings of adult butterflies reflect the isotopic traits of the plants they consumed while in the caterpillar stage,” Shipilina explains. Isotopes are variations of the same chemical element, sharing similar chemical properties but differing in atomic mass.
Co-first author Megan Reich and Clement Bataille from the University of Ottawa dedicated years to developing this technique, testing different isotopes, refining statistical methods, and applying machine-learning techniques to bolster accuracy and clarity.
The analysis highlighted variability in travel behavior among the butterflies: some embarked on long migrations southward from Scandinavia, traversing the Sahara, while others simply migrated short distances, remaining in the Mediterranean region north of the desert.
Is it in their genes?
The researchers then performed whole genome sequencing to compare the DNA sequences of each individual butterfly. Surprisingly, they found no genetic differences between the butterflies that traveled long distances and those that migrated shorter distances.
“This discovery contrasts sharply with patterns observed in certain birds, another extensively studied migratory group,” explains Shipilina. “For instance, in willow warblers, a large chromosomal region correlates with differing migratory directions, revealing how various phenotypes can emerge from distinct genomic profiles.” Moreover, migration behaviors in painted ladies could not be linked to sex, wing size, or wing shape.
Painted ladies adapt to the environment
The researchers suggest that a concept called phenotypic plasticity might clarify the different migration behaviors. “Phenotypic plasticity is an organism’s ability to alter its phenotype—in this instance, its long- or short-distance migration—based on environmental conditions without changing its genetic structure,” Shipilina clarifies.
For example, during summer, butterflies in Sweden may feel compelled to migrate long distances southward across the Sahara due to rapid changes in day length or other seasonal signals. Conversely, those in Southern France, where days are longer, may not encounter similar migratory cues and thus undertake only short-distance journeys in the Mediterranean.
In comparison to other butterflies, such as the well-explored monarch, much about painted ladies’ migrations remains elusive. Does this observed pattern extend across their extensive geographic range? Is this behavior unique to butterflies, or could it manifest in other insects as well? ISTA researcher Daria Shipilina and her team are committed to filling these knowledge gaps—one study at a time.
