Evolution, the process through which animals and other living organisms change their inherited traits over time, typically unfolds slowly over thousands or even millions of years. Some species, however, can adapt at a faster pace, particularly when they are isolated from other species and in new environments.
Researchers at Université Savoie Mont Blanc-INRAE in France recently showed that two populations of Arctic charr (Salvelinus alpinus), cold-water freshwater fish related to salmon and trout, evolved differently after being separated for just under a century. Their paper, published in Proceedings of the Royal Society B, suggests that, when isolated, some animals might be able to adapt to changes in their environment faster than previously anticipated.
"This natural experiment provided a unique opportunity to investigate how rapidly populations can diverge after being introduced into a contrasting environment, and to better understand the processes underlying this divergence," Hervé Rogissart, first author of the paper, told Phys.org.
"More specifically, we wanted to determine whether the observed differences were primarily driven by phenotypic plasticity, which allows organisms to adjust their phenotype to local environmental conditions, or whether they also reflected genetic changes driven by natural selection over successive generations."
Studying two Arctic charr populations
Rogissart and his colleagues observed two distinct wild Arctic charr populations with the same ancestry that had become isolated from each other less than 100 years ago. The first population lived in Lake Geneva, a deep peri-Alpine lake on the northern side of the Alps, while the second was introduced into Lake Allos, an Alpine lake in Mercantour National Park.
The team first studied adult fish from each population, comparing their morphology (i.e., their body shape and structure), as well as their growth under natural conditions. They then studied new fish raised in a separate controlled environment.
"During the spawning season, we also collected gametes from these adults to produce offspring, which were then reared under identical conditions in a common garden experiment," Rogissart explained. "We measured several phenotypic traits in these juveniles, including morphology and growth, and assessed their metabolism under both normal and thermally stressful conditions. This allowed us to distinguish environmentally induced differences from those with a genetic basis."
By observing distinct adult Arctic charr populations in the wild, examining their offspring in a common controlled environment and conducting genetic analyses, the researchers were able to gather new insights into their evolution. Specifically, they could determine the extent to which phenotypic plasticity and genetic divergence contributed to the observed differences between the two populations residing in Lakes Geneva and Allos.
"We found marked differences in morphology and growth between wild adults, which were expected given the contrasting environments and the role of phenotypic plasticity," Rogissart said. "More importantly, although differences in morphology were subtle and growth differences became evident only after analyzing a larger number of juveniles, juveniles reared under common garden conditions exhibited clear metabolic differences, suggesting rapid physiological adaptation despite the populations sharing a common origin less than a century ago."
Possible implications for conservation efforts
The results of this study suggest that natural selection and the ability of a single genetic makeup to produce different traits can both contribute to the rapid adaptation of fish to a specific environment. The rapid evolution observed by the team is striking, as it suggests that some species have greater adaptive potential than anticipated.
"Our results showed that most of the differences in morphology and growth can be explained by phenotypic plasticity, suggesting that fish rapidly adjust to local environmental conditions such as food availability and temperature," Rogissart explained. "In contrast, juvenile fish from Lake Allos displayed a higher metabolic rate and a different relationship between metabolism and body mass at elevated temperatures, even when raised under identical conditions."
The Arctic charr populations observed by Rogissart and his colleagues changed their physiological and metabolic traits within just a few decades. These changes may have allowed them to survive and thrive in the two alpine lakes they inhabit, which are at different altitudes. Future studies could draw inspiration from these findings and explore the evolution of other fish or animal species that live in isolation in distinct natural environments.
"In the context of climate change, our findings provide new insights into how genetic diversity and population history shape variation in traits and thermal responses among populations, ultimately influencing their capacity to cope with environmental change," Rogissart added. "Our next step will be to investigate the genetic basis of adaptation to climate change. By studying genetic diversity across a larger number of Arctic charr populations, we hope to identify genomic signatures of adaptation and the candidate genes involved in coping with rising water temperatures under climate change."
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Publication details
Hervé Rogissart et al, A century of allopatry: plasticity and rapid selection shape phenotypic trait variability under contrasting environments, Proceedings of the Royal Society B: Biological Sciences (2026). DOI: 10.1098/rspb.2026.0692
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Citation: Two Arctic charr populations evolved in less than a century, study finds (2026, July 30) retrieved 30 July 2026 from https://phys.org/news/2026-07-arctic-charr-populations-evolved-century.html
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