Global warming is disrupting the ecological balance of the Arctic, directly threatening the survival of polar bears. These predators depend on sea ice to hunt, move and reproduce. However, the accelerated melting of the ice reduces their vital territory every year. Faced with this environmental pressure, a study conducted by researchers at the University of East Anglia (United Kingdom) and published in the journal Mobile DNA reveals an unexpected biological response: a modification of genetic activity in polar bears from southeast Greenland, exposed to higher temperatures and a more unstable habitat.
Analysis of their DNA shows the massive activation of transposons — mobile elements of the genome — associated with key functions such as metabolism or response to heat stress. This mechanism could reflect an attempt at rapid adaptation in the face of an increasingly hostile environment.
A subgroup of polar bears facing a radically different climate
In southeast Greenland, a small group of polar bears live in conditions very different from those of other populations of the species. This territory, located outside the heart of the Arctic, has a milder climate, but also more unstable. There is heavy rainfall, deep fjords, and forest-tundra cover. According to data from the Danish Meteorological Institute, this region has much higher average temperatures than northeast Greenland. In Tasiilaq, for example, temperatures can vary from -30°C to +26°C. While to the north, at Station Nord, they remain much colder.
This southern zone, marked by a rapid reduction in sea ice, exposes bears to a scarcity of hunting platforms on the ice. This forces individuals to adapt their behavior, their movements and potentially their diet. This extreme environmental context proves crucial. Researchers see this as a projection of the climate that all polar bears will face by the end of the century.
The group studied consists of bears isolated for around 200 years due to coastal currents. It only benefits from very limited contact with other populations, thus limiting genetic mixing. This isolation factor accentuates the selective pressure on their genomes.
This unique configuration piqued the interest of the University of East Anglia team. Scientists have undertaken an in-depth analysis of the genetic activity of these southern bears, in order to identify possible traces of adaptation to this warmer climate. These animals represent a rare opportunity to observe evolution in real time in the context of accelerated climate change.
Unusual genetic activity linked to temperature
The study was thus based on transcriptomic analyzes carried out from blood samples from 17 adult bears. More precisely: 12 from northeast Greenland (NEG), and 5 from the southeast (SEG). This data, initially collected by the University of Washington, was reinterpreted by Godden's team with a more sensitive statistical model. It notably integrates local climate data as an independent variable, underlines the university press release.
The researchers observed a strong activation of transposons, or “jumping genes”. These are fragments of DNA capable of moving through the genome and modifying its expression. In the southeastern population, more than 1,500 transposons were expressed differently compared to the northern bears. The most active transposons belong to the LINE and LTR families. We know its families for their role in genetic regulation and the evolution of genomes in mammals.
Temperature clearly proved to be a central explanatory factor. By adding temperature records from 2016 (the year before the samples were taken), the scientists found that the intensity of transposon expression followed a trend correlated with local climatic conditions. Southern bears showed a greater proportion of young transposons—evidence of recent and rapid mobilization.
These genetic elements have been identified in functional areas of the genome, including coding regions. This means that transposons are not just present. They actively interact with genes regulating functions crucial for survival. The location of certain transposons on the X chromosomes, and their absence on the Y, confirms a differentiated expression depending on sex, taken into account in the analyses.
Key genes activated in southeastern bears
Beyond transposon activity, scientists also identified clear differences in the expression of several genes between the southeastern (SEG) and northeastern (NEG) populations. By integrating temperature as a covariate, they highlighted 27 genes whose activity differed in a statistically significant manner.
© Alice Godden and Benjamin Rix
Bear distribution and local temperatures.
Some of these genes are linked to known heat stress response mechanisms. For example, genes HSPA4L
And HSPH1 encode heat shock proteins. Genes essential for the folding and protection of cellular proteins in the event of excessive heat. Other genes, such as
RSAD2an antiviral gene also called
ViperinOr ACTR2involved in coagulation, indicate more systemic adaptations.
Particularly interesting, ten of these differentially expressed genes overlap with transposon loci. This suggests that transposon activity could have direct functional consequences on the bear phenotype. Among these genes are SHANK1 (involved in cell signaling), BBS12 (associated with ciliated functions) or even non-coding RNAs (lncRNAs) as
LOC121104823which play a role in epigenetic regulation.
These changes are not just anecdotal. They affect entire biological pathways. Functional analysis revealed involvement in the regulation of ionic balance, lipid dehydration, and specific immune responses. All of these results indicate an integrated response of the genome to environmental constraints.
These genetic adjustments could represent a form of rapid adaptation, although not guaranteed in the long term. However, they offer a concrete basis for considering the biological resilience of certain subgroups of polar bears, linked to their environment.
An avenue for conservation, but not a solution
Identifying a potential genetic response of southeastern bears to a warmer climate might seem hopeful. However, the authors of the study emphasize caution in an article from The Conversation. Alice Godden specifies: “This apparent adaptation does not mean that polar bears are safe from extinction. » This is not a universal saving mutation, but a local dynamic, observed in an isolated group.
This Greenland subgroup has been genetically distinct for about two centuries. A fact which favored the emergence of adaptive singularities. But also increased vulnerability to loss of diversity. The observed adaptation is based on mobile genetic elements, which can, of course, generate variability, but also introduce instabilities into the genome.
The researchers also point out that the analysis was carried out using blood samples, therefore somatic tissues. However, for these adaptations to be transmitted to future generations, it would be necessary to demonstrate similar activity in germ cells. Furthermore, these genetic changes, as dramatic as they are, do not compensate for the rapid loss of Arctic ecosystems.
The study provides a valuable contribution to guide conservation policies. By identifying genetically distinct and potentially more resilient populations, it allows monitoring and protection efforts to be targeted. But above all it reminds us that only a massive reduction in greenhouse gas emissions will make it possible to preserve the minimum conditions of survival for the entire species.
“These results should not serve as an alibi for inaction. But rather alert on the speed of the upheavals underway”concludes Simone Immler.
Source: Alice M. Godden et al., “Diverging transposon activity among polar bear sub-populations inhabiting different climate zones”. Mobile DNA (2025).
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