An international team led by the Barcelona Botanical Institute (IBB, CSIC-CMCNB), in collaboration with the Institute of Evolutionary Biology (IBE, CSIC-UPF) and collaborators from Africa, Europe and the United States, has discovered that cardera butterflies (Vanessa cardui) make opposite migrations in each hemisphere. … of the Earth. While populations in the northern hemisphere fly south during the northern fall (between September and December), those in the southern hemisphere move in the opposite direction during the southern fall (between March and June), following their own seasons. This surprising pattern, unprecedented in insects, has a genetic basis associated with chromosomal inversion, as demonstrated in a study published in Nature Communications.
This discovery represents the first documented case of “migratory division” in insects, a phenomenon well known in birds, but until now never confirmed in these animals. In these divisions, populations of the same species develop different migratory strategies, which can lead to their isolation and, possibly, to the formation of new species.
Two hemispheres, two migrations
In previous studies, the same group showed that Vanessa Cardui It carries out the longest migrations known among butterflies, in a circuit of up to 15,000 kilometers between equatorial Africa and Europe. Now the team has identified a new migratory circuit in the southern hemisphere of Africa, completely independent of the route taken in the northern hemisphere. The group of researchers traveled the African continent in search of the cardigan butterfly and analyzed the DNA of more than 300 specimens from 38 countries in Africa and Europe. Genomic analyzes revealed a large fragment of inverted DNA, or chromosomal inversion, on chromosome 8. This region, distinct in individuals from each hemisphere, contains genes linked to migratory behavior.
“We observed that southern populations do not cross the equator, but rather follow their own cycle adapted to the seasonality of the southern hemisphere. The chromosome inversion contains a receptor for the neurotransmitter GABA-B, involved in orientation during flight. Our results highlight a key point in the genetic basis of navigation,” explains Aurora García-Berro, researcher at the Barcelona Botanical Institute (IBB, CSIC-CMCNB) and first author of the study.
The team proposes that this chromosomal inversion changes the way butterflies interpret environmental signals. “We know thanks to the monarch butterfly that migratory butterflies, but also other insects, orient themselves using the magnetic field and the position of the sun. The response to these parameters should be opposite in the two hemispheres. Our hypothesis is that movement patterns are limited within each hemisphere thanks to specifically adapted orientation mechanisms,” explains Daria Shipilina, researcher at Uppsala University (Sweden) and co-author of the work.
The equator, an unexpected evolutionary barrier
Gérard Talavera, principal researcher at the BWI CSIC and leader of the study, explains how this invisible border between the hemispheres could act as an evolutionary barrier, limiting genetic exchanges between migratory populations and promoting their diversification: “Unlike birds, the division we see is latitudinal. The equator could provide a barrier to the migration of other butterflies and even other groups of migratory animals. This could explain why some sister species live in opposite hemispheres. “The migratory divide we discovered could be a previously unnoticed evolutionary driver.”
Insect migrations have enormous ecological importance globally. As pollinators, they connect ecosystems separated by thousands of kilometers, even between continents; They serve as food for other species, they can become agricultural or forestry pests and, in some cases, act as vectors of parasites. Understanding how these insects interpret environmental signals and guide their migrations allows us to unravel the genetic bases of complex behaviors and better understand the ecological role of migratory insects.
The study also highlights the importance of analyzing biological patterns and processes on a global scale, particularly in the southern hemisphere, which is less represented in biodiversity studies. 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.
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