Context:
A recent study published in PNAS Nexus, led by evolutionary biologist Daria Shipilina, investigates the migration patterns of the painted lady butterfly (Vanessa cardui). The research provides crucial insights into the genetic and environmental factors influencing one of the longest insect migrations in the world.
About painted lady butterfly:
· The painted lady butterfly (Vanessa cardui), also known as the thistle butterfly, is native to Canada but cannot survive in colder climates.
· It is a long-distance migrator, traveling up to 9,000 miles, often crisscrossing the Sahara between Europe and sub-Saharan Africa.
· The butterfly has orange wings with black tips, with white spots and black lines on its forewings. It closely resembles the American lady butterfly but can be distinguished by its four eyespots on the hindwings instead of two.
· Highly adaptable, V. cardui thrives in diverse habitats, from seashores and gardens to mountaintops. It is one of the most widely distributed butterflies, though it is absent from South America.
Multi-Generational Migration Cycle
Studying insect migration has been challenging due to their small size and tracking limitations. However, advances in genomics and miniaturized tracking now allow precise analysis.
· The painted lady butterfly (Vanessa cardui) migrates up to 15,000 km in a multi-generational cycle spanning 8–10 generations, with each butterfly living only two to four weeks.
· In spring, they migrate north from the Sahara to breed in southern Europe, and by late summer and autumn, their offspring return southward. Their strong thoracic muscles enable long-distance flight, making them exceptional migrators.
Genomic and Isotopic Analysis
To track their migration, researchers used stable isotope analysis, examining hydrogen and strontium isotopes embedded in their wings. Since butterfly wings do not undergo metabolic changes, they retain isotopic signatures from the food and water consumed during the larval stage.
· By comparing isotope ratios with geographical isoscapes (maps of isotope distributions) from Europe and North Africa, scientists estimated the distances traveled by individual butterflies.
· Genetic analysis revealed that short- and long-distance migrants do not form distinct genetic groups. Instead, all painted lady butterflies belong to a single interbreeding population, indicating that environmental factors play a more significant role in migration than genetic differences.
· Additionally, wing size and shape did not significantly impact migration distances, and wing wear—a common indicator of travel length—was not always correlated with greater migration distances.
Conclusion:
The study challenges assumptions about migration genetics, highlighting the role of environmental conditions in butterfly movement. Future research will examine genetic variations in V. cardui across regions like the UK and Japan and explore migration in diverse environments. Understanding these factors is crucial for predicting climate change impacts on migration, advancing a comprehensive framework for insect migration studies.
