A study by the Botanical Institute of Barcelona (CSIC) reveals how the transoceanic migration of the butterfly Vanessa atalanta during the last glacial period from North America impacted biodiversity in Eurasia.
The majority of animal species have relatively continuous geographic distributions. However, there are surprising exceptions in which sister species or populations of the same species inhabit geographically distant regions with no apparent connection. How can a butterfly species from India (Vanessa indica) have its sister species in the Canary Islands (Vanessa vulcania), more than 7,000 km away?
These enigmatic distributions, known as disjunct distributions, have fascinated and puzzled biologists and biogeographers for decades. A new study led by scientists from the Botanical Institute of Barcelona (IBB, CSIC-CMCNB), and published in Molecular Ecology, reveals how a migratory butterfly, Vanessa atalanta, crossed the Atlantic some 21,000 years ago and displaced another species, Vanessa indica, from Europe to Asia.
A transoceanic migration with ecological consequences
Thanks to the genomic analysis of dozens of butterflies from the genus Vanessa, researchers determined that V. atalanta has two well-differentiated disjunct populations: one in North America and another in Europe. Through demographic models, genetic diversity analyses, and the fact that its sister species is endemic to Hawaii, researchers concluded that the species originated in America, from where it crossed the Atlantic Ocean during the last glacial maximum about 21,000 years ago. The cold climate conditions of that period, combined with a contraction of its habitat, likely forced changes in its distribution and facilitated a transoceanic jump to southern Europe or North Africa, where conditions were favorable for settlement.
Once in Europe, V. atalanta likely came into contact with V. indica, a species then present on the continent. Although today both species are separated by thousands of kilometers, researchers found clear genetic signals of hybridization, which can only be explained if they coexisted in the past. Using ecological distribution models, the study proposes that the arrival of V. atalanta triggered competition between species that ultimately pushed V. indica eastward, confining it to its current distribution in Asia.
Just a few months ago, this research team documented “in flagrante delicto” and for the first time how a group of butterflies crossed the Atlantic from Africa to South America. Now, they demonstrate the ecological consequences of a similar dispersal event in the past.
This research is an example of how genetics, biogeography, and ecology can be combined to solve major evolutionary puzzles. The study represents a significant advancement in understanding how large-scale dispersal and interspecies interactions shape the evolutionary history and biogeography of global biodiversity.
Reference article:
Palahí A, García-Berro A, Dincă V, Vodă R, Dapporto L, Backström N, Vila R, Pierce NE, Talavera G (2025). Trans-Atlantic Dispersal and Introgression Explain Holarctic Disjunct Distributions in Vanessa Butterflies. Molecular Ecology.
https://onlinelibrary.wiley.com/doi/full/10.1111/mec.17781