Butterfly migration habits are not determined by their DNA

Each year, painted lady butterflies embark on one of the most remarkable migrations in the animal kingdom, traveling up to 10,000 km between Africa and Europe in search of optimal breeding conditions. 

But what determines how far an individual butterfly will travel? Is migration encoded in their DNA, or is it shaped by external factors?

A recent study, led by scientists at the Institute of Science and Technology Austria (ISTA) in collaboration with international research teams, reveals that environmental conditions – not genetics – dictate whether a painted lady will travel long or short distances. 

The findings challenge previous assumptions about butterfly migration and highlight the role of phenotypic plasticity – the ability of organisms to alter their behavior in response to their surroundings.

Study co-author Daria Shipilina is an evolutionary biologist and postdoctoral researcher at ISTA. 

“The painted lady is a strikingly beautiful and colorful butterfly species,” said Shipilina. “Watching them form large aggregations is a true spectacle. But what makes them particularly special is their incredible long-distance migrations.”

One of nature’s most impressive migrations

Painted ladies begin their journey in Northwest Africa in the spring. They fly across the Mediterranean into Europe, where subsequent generations continue northward, reaching as far as Sweden and the Arctic tundra. 

For a long time, scientists believed that once these butterflies arrived in northern Europe, they perished in the colder months. 

However, recent studies confirmed that painted ladies complete a circular migration, returning south in autumn – some staying in the Mediterranean region while others venture all the way back to Africa, even crossing the Sahara.

This discovery raised a crucial question: why do some painted ladies migrate farther than others? Do they have an internal navigation system that dictates their path?

To investigate, Shipilina and her team collected painted lady butterflies from various locations, including Benin, Senegal, Morocco, Spain, Portugal, and Malta, and employed advanced isotope geolocation techniques to track their movements.

Tracing the butterflies’ origins and destinations

By analyzing the stable isotopes in butterfly wings, the researchers could determine where each butterfly originated as a caterpillar.

“The key principle of this method is that the isotopic makeup – or the stable isotopes – of the adult butterfly’s wings mirrors the isotopic signature of the plants they ate as a caterpillar,” Shipilina explained.

Co-first authors Megan Reich and Clément Bataille from the University of Ottawa spent several years refining this geolocation technique, integrating machine-learning algorithms to improve accuracy. 

The analysis revealed two distinct migration patterns: while some butterflies took a long trip south, migrating from Scandinavia across the Sahara, others traveled shorter distances, staying in the Mediterranean region.

This raised another question – was this difference encoded in the butterflies’ genes?

Genetic basis of butterfly migration 

To investigate the genetic basis of migration, the scientists conducted whole genome sequencing on the butterflies. Surprisingly, their analysis showed no significant genetic differences between those that migrated long distances and those that stayed closer to Europe.

“This finding fundamentally differs from what is observed in some birds, another well-studied migratory group,” Shipilina noted. “For example, in willow warblers, a large chromosomal region has been associated with variable migratory direction, illustrating how different phenotypes arise from distinct genomic compositions.”

Additionally, factors like sex, wing size, and wing shape had no clear influence on migration distances, further ruling out genetic or physiological predisposition.

Environmental cues and butterfly migration

If genes don’t dictate migration behavior, then what does? According to the study, environmental conditions play the dominant role. 

The scientists propose that phenotypic plasticity – the ability of an organism to adapt its behavior based on external cues – explains why some butterflies migrate farther than others.

For instance, a butterfly in Sweden might receive strong environmental cues to migrate long distances, such as shortening day length and temperature drops, prompting it to cross the Sahara. 

Meanwhile, a butterfly in Southern France, where seasonal changes are less extreme, may not experience the same triggers, leading it to migrate only as far as the Mediterranean region.

“Phenotypic plasticity allows organisms to adjust their migratory behavior without changing their genetic makeup,” Shipilina said. “This flexibility could be key to how painted ladies adapt to different climatic conditions.”

Complexities of butterfly migration 

Compared to species like monarch butterflies, painted lady migration remains relatively understudied. 

This latest research raises new questions: Does this migration pattern apply to painted ladies worldwide? Are other butterfly species also influenced by environmental cues rather than genetics? How will climate change impact the migration patterns of painted ladies in the future?

The researchers aim to build on these findings to further unravel the complexities of butterfly migration.

“There is still so much to learn about the migration of painted ladies,” Shipilina said. “We are determined to close this knowledge gap – one paper at a time.”

By demonstrating that migration strategies are shaped by the environment rather than hardwired in DNA, this study provides a new perspective on how insects navigate the world. 

As climate patterns shift, understanding these flexible behaviors may be critical for predicting and protecting the future of migratory butterflies.

The study is published in the journal PNAS Nexus.

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