Wings across continents: The epic 4,000-kilometer odyssey of the Painted Lady Butterfly

Scientists from the University of Ottawa, Uppsala University, the Institut Botànic de Barcelona, and other institutions have tracked the migratory feats of the painted lady butterfly (Vanessa cardui). These seemingly delicate creatures defy expectations, with remarkable variation in their migratory behaviour. The study reveals that while some individuals are embarking on a breathtaking 4,000-kilometer trek from Scandinavia to the heart of sub-Saharan Africa, crossing both the Mediterranean Sea and the daunting expanse of the Sahara Desert, others journey short distances, halting at the Mediterranean.

Clement Bataille, Associate Professor at uOttawa’s Faculty of Science, highlighted their method: “By analyzing hydrogen and strontium isotopes, we traced these butterflies back to their origins and estimated how far they had travelled, confirming distinct migratory behaviours.”

Earlier research had shown that the Vanessa cardui could travel 4,200 km across the ocean from West Africa to French Guiana, South America.

“Interestingly, this variation in migration distance isn't due to genetic differentiation, rather, we think it is due to a flexible response to environmental signals, like photoperiod. Our findings highlight how environmental factors may be dictating migratory behaviors in insects,” emphasized Megan Reich, Postdoctoral Fellow in the Department of Biology at the University of Ottawa and co-lead author of the study.

The team collected these butterflies from diverse locations across Europe and Africa between 2018 and 2019. They conducted cutting-edge isotope analysis in Canada and genomic sequencing in Spain and Sweden. The results illuminate a migration pattern, where butterflies from the north journey further south than their southern peers during early autumn. Related research further describes this leapfrog migration pattern.

“These findings raise important questions: Does this pattern of no genetic differentiation despite variation in migratory behaviour hold across the broad geographic distribution of the painted lady butterfly? Is this phenomenon unique to butterflies? Investigating these questions will deepen our understanding of how migration evolves and is maintained across species,” adds Daria Shipilina, Postdoctoral Researcher at the Institute of Science and Technology, Austria, and co-lead author of the study.

Migratory insects are crucial to ecosystems, transporting biomass and nutrients and serving as pollinators and a food source for other species. Reich pointed out, “Understanding insect migratory patterns is crucial for conservation and for biosecurity. Future studies are needed to confirm the connection between migration distance and environmental conditions and, importantly, identify the triggers of insect migration. This work is vital because it will allow us to predict how human-driven changes to the environment may impact insect migration in the future.”

The study is published in PNAS Nexus titled “Isotope geolocation and population genomics in Vanessa Cardui: Short- and long-distance migrants are genetically undifferentiated.” It marks a significant advance in understanding insect migration and its importance for biodiversity conservation amid global environmental shifts.