This pattern, discovered in the painted lady butterfly (Vanessa cardui), had never been documented in insects before
The butterfly Vanessa cardui was the protagonist of the discovery (Photo: Gerard Talavera)
An international team led by the Botanical Institute of Barcelona (IBB, CSIC-CMCNB), with the participation of the Institute of Evolutionary Biology (IBE, CSIC-UPF) and collaborators from Africa, Europe and the United States, has discovered that painted lady butterflies (Vanessa cardui) undertake opposite migratory routes in each hemisphere of the Earth. While populations in the Northern Hemisphere fly southward during the boreal autumn, those in the Southern Hemisphere move in the opposite direction during the austral autumn, following their own seasonal cycles.
This striking pattern —unprecedented in insects— has a genetic basis linked to a chromosomal inversion, as reported in a study published in Nature Communications.
The finding represents the first documented case of a migratory divide in insects, a phenomenon well known in birds but never before confirmed in this group. In such divisions, populations of the same species develop different migratory strategies, which can lead to reproductive isolation and, ultimately, the emergence of new species.
Two hemispheres, two migrations
Previous research by the same team showed that Vanessa cardui carries out the longest migrations known among butterflies, traveling up to 15,000 kilometers in a circuit between equatorial Africa and Europe. The new study identifies an additional migratory circuit in southern Africa that is completely independent from the northern one.
To uncover this pattern, the researchers traveled across the African continent in search of the painted lady butterfly and analysed the DNA of more than 300 specimens from 38 countries in Africa and Europe. Genomic analyses revealed a chromosomal inversion of 9 million base pairs on chromosome 8. This region -wich differs between individuals from each hemisphere,- contains genes linked to migratory behavior.
“We observed that southern populations do not cross the equator, but instead follow their own cycle adapted to the seasonality of the Southern Hemisphere. The chromosomal inversion includes a GABA-B neurotransmitter receptor, wich is involved in orientation during flight. Our results point to a key component of the genetic basis of navigation,” explains Aurora García-Berro, researcher at the Botanical Institute of Barcelona (IBB, CSIC-CMCNB) and first author of the study.
Aurora García-Berro, researcher at the Botanical Institute of Barcelona (IBB, CSIC-CMCNB) and first author of the study. (Photo: Gerard Talavera)
The team suggests that this chromosomal inversion alters how butterflies interpret environmental cues. “We know from studies on the monarch butterfly, that migratory butterflies, and other insects as well, orient themselves using the magnetic field and the position of the sun. Responses to these cues must be reversed between hemispheres. Our hypothesis is that movement patterns are constrained within each hemisphere by orientation mechanisms that are specifically adapted to those conditions,” says Daria Shipilina, researcher at Uppsala University (Sweden) and co-author of the study.
The equator: an unexpected evolutionary barrier
Gerard Talavera, CSIC senior scientist at the IBB and leader of the study, explains how this invisible border between hemispheres could act as an evolutionary barrier, limiting gene flow between migratory populations and promoting diversification:
“Unlike birds, the division we observe is latitudinal. The equator could act as a barrier to migration for other butterflies and even for other migratory animals. This could help explain why closely related species are found in opposite hemispheres. The migratory divide we have uncovered may represent an evolutionary driver that has so far gone unnoticed.”
The ecological importance of migration
Insect migrations play a crucial role in ecosystems worldwide. As pollinators, insects connect ecosystems separated by thousands of kilometers, even across continents. They serve as food for other species, can become agricultural or forestry pests, and in some cases act as vectors of parasites. Understanding how insects interpret environmental signals and orient their migrations helps unravel the genetic basis of complex behaviors and provides deeper insight into the ecological role of migratory insects.
The study also highlights the importance of examining biological patterns and processes at a global scale, particularly in the Southern Hemisphere, which remains underrepresented in biodiversity research. To this end, the research team at the Botanical Institute of Barcelona (IBB, CSIC-CMCNB) continues to study the genomes of other migratory species distributed from southern Africa to Europe.
The study has been published in the journal Nature Communications and is available at:
García-Berro A, Shipilina D, Backström N, Suchan T, Palahí A, Collins S, Martins D, Pierce N, Vila R & Talavera G (2025). A north-south hemispheric migratory divide in the butterfly Vanessa cardui. Nature Communications.