Image Caption: Visual representation of the parallel selection on MHC immune genes in aquaculture-raised Atlantic salmon from Norway (right) and North America (left). Despite genome-wide divergence, both populations show selection signals in the same region of the genome.
(Image credit: GBE-240806.R2.png)
Summary: Atlantic salmon populations in Norway and North America, though genetically distant due to ancient divergence, show signs of selection on the same immune gene region under aquaculture conditions. A new study from CIGENE suggests that domestication environments can drive convergent responses in long-separated populations.
Body: Atlantic salmon (Salmo salar) populations in Europe and North America have been evolving separately for thousands of years, resulting in marked genetic differences across their genomes.
However, the new study led by researchers at CIGENE and Université de Perpignan Via Domitia (France) reveals that aquaculture breeding in both regions has favored the same ancestral immune gene variants—specifically within a region known as the Major Histocompatibility Complex (MHC), which plays a key role in recognizing pathogens.
“We were surprised to find that the same immune variants, despite being ancient, were independently selected in aquaculture populations on both sides of the Atlantic,” said Celian Diblasi, co-lead author and a PhD student at CIGENE. “It shows that similar farming conditions can repeatedly favor the same genetic variants, even in lineages that diverged long ago.”
MHC regions are known for maintaining high genetic diversity, a phenomenon called balancing selection, where multiple alleles are retained over time due to their advantages against different pathogens. In this case, aquaculture environments may have tipped the balance toward specific variants, favoring the same immune strategies in distinct populations.
“It’s fascinating to see parallel selection emerge from shared ancestral diversity,” said Pauline Buso, co-lead author and a master’s intern from France to NMBU. “It gives us a glimpse into how evolution can repeat itself under similar pressures.”
The study also examines the role of ancient whole-genome duplication in Atlantic salmon, which left many genes in pairs. Some of these gene duplicates appear to have been shaped independently by selection in both populations, suggesting a flexibility in the salmon genome.
“This shows that long-standing genomic features still shape ongoing adaptation today,” Marie Saitou, the senior author at NMBU, added. “It deepens our understanding of how complex genomes respond to domestication.”
An illustration accompanying the study visualizes how selection on the same immune region has occurred independently in Norway and North America.
More about the study: This research was conducted in collaboration between NMBU and Université de Perpignan Via Domitia (France). This study was carried out as part of Pauline Buso’s Master’s thesis in Functional Biology and Ecology, supported by the EUR TULIP Graduate School and the French National Research Agency (ANR) through the “Investing for the Future” program (grant ANR-18-EUR-0019).
The research was also supported by the Research Council of Norway (grant nos. 325874, 275310, and 221734), and PhD funding from the Faculty of Biosciences, Norwegian University of Life Sciences (NMBU).
Read the article in full: Genome Biology and Evolution, Volume 17, Issue 4, April 2025, evaf063, https://doi.org/10.1093/gbe/evaf063