Researchers at Bangor University found that consistently mild winters made common wall lizards more active during hibernation and were associated with signs of oxidative-stress-related DNA damage. The study compared cold, constantly mild, and fluctuating winter regimes over 3.5 months and found that fluctuating temperatures did not produce the same DNA effects. Scientists warn these hidden molecular costs could shorten lifespans and reduce reproductive success and call for models to include physiological stress markers, not just visible behavior or population counts.
Mild Winters May Damage Lizard DNA and Undermine Ecosystems, Study Warns
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Winter has long been a biological pause for hibernating animals — a time when reduced activity helps conserve energy. New research from Bangor University suggests that increasingly mild winters can erode that pause, producing subtle but potentially serious physiological damage in common wall lizards.
Study Design and Key Findings
The research team exposed common wall lizards to three simulated winter regimes over a three-and-a-half-month hibernation period: a typical cold winter, a consistently mild winter, and a winter with fluctuating temperatures. Scientists tracked activity, body condition and markers of oxidative stress — a form of cellular damage that occurs when free radicals overwhelm antioxidant defenses and can harm cells and DNA.
Compared with lizards kept in cold conditions, those held under consistently mild winter temperatures were significantly more active during hibernation and showed a trend toward increased DNA damage consistent with oxidative stress. By contrast, lizards exposed to fluctuating winter temperatures did not show the same pattern of DNA harm.
"Winter is warming faster than summer, posing a substantial threat to hibernating ectotherms, whose physiology depends directly on environmental conditions," said lead author Miary Raselimanana.
Why This Matters
Hibernation conserves energy when food is scarce. If milder winters force animals to become more active at a time when resources remain limited, they may deplete vital reserves and be unable to fully recover. Over time, that hidden physiological cost could shorten lifespans, reduce reproductive success and impair population resilience.
Those effects extend beyond reptiles. Ectotherms (cold-blooded animals) support ecosystem services such as pest control, pollination and contributions to biodiversity. Subtle physiological stress across these groups could cascade through food webs and affect agriculture, ecosystem stability and human communities that rely on these services.
"The specific warming patterns most disruptive to hibernation, their effects on winter activity, and the subsequent physiological consequences are poorly understood," Raselimanana added, noting that behavior alone can mask deeper molecular impacts.
Study supervisor Dr. Kirsty Macleod emphasized the mixed picture: "Overall, our findings suggest resilience in the behavior of common wall lizards to moderate winter warming. However, hidden costs at a molecular level could emerge under sustained mild conditions."
Next Steps
The authors call for future studies and predictive models to incorporate physiological markers such as oxidative stress, not just visible behavior or population counts. That broader approach would help conservationists, planners and policymakers better identify species at risk as winters warm.
While the research focuses on common wall lizards, the main takeaway is broader: small shifts in seasonal timing and temperature can erode biological systems that developed over millennia, with potential consequences for environmental resilience and food security.
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