Wild Mammals Reveal Surprising Sex and Habitat Twists in Cellular Aging

Rapid early-life growth in wild mammals carries a hidden cellular price tag, but whether it actually shrinks the protective caps at the ends of chromosomes depends heavily on sex and environmental quality. While scientists traditionally assumed that growing up fast universally accelerates aging by shortening telomeres, a team of researchers has found that this relationship is far more complex in nature. The findings demonstrate that sex differences and habitat harshness shape how juvenile development impacts cellular health.

To untangle why past studies on animal growth and telomeres produced conflicting results, Florentin Remot and colleagues performed an updated systematic literature synthesis covering 46 studies across various wild vertebrates. The results, published in Philosophical Transactions of the Royal Society of London Series B Biological Sciences, showed that exactly half of the previously reported relationships between body growth and telomere length were not statistically significant, while one-third were negative and the rest were positive. This lack of broad consensus prompted the team to look closer at large herbivores.

How Wild Sheep Reveal Hidden Sex Differences in Cellular Aging

The researchers investigated two intensively monitored wild ungulate populations, starting with Soay sheep living on the remote St Kilda archipelago in Scotland. Because Soay rams experience intense mating competition, males must grow much larger and faster than females during their first four months of life. The team tracked birth mass, juvenile mass at four months, and relative telomere length from blood samples of 841 individual lambs.

The analysis revealed that rapid postnatal mass gain correlated with shorter telomeres in male lambs, but showed no such effect in females. However, males that were heavier at birth appeared buffered against this rapid growth cost. Male lambs with a higher birth mass possessed longer telomeres, suggesting that greater early maternal investment helps cushion the cellular toll of subsequent fast growth.

Why Rich Habitats Can Bring Unexpected Costs for Roe Deer

The researchers also evaluated European roe deer across two contrasting French forest populations managed by the Office Français de la Biodiversité. Trois-Fontaines offers a high-quality environment with rich soil and abundant food, whereas Chizé represents a resource-limited habitat prone to summer droughts. By examining telomere length in relation to winter fawn mass, the team discovered that heavier fawns at eight months old had shorter telomeres only in the high-quality environment of Trois-Fontaines.

In the harsher environment of Chizé, fast growth and heavy weights were largely absent, and no negative relationship with telomere length emerged. This unexpected pattern suggests that when fawns reach their maximal physiological growth potential in rich habitats, the intense metabolic pace increases oxidative damage and accelerates telomere attrition. By contrast, environmental constraints in poorer habitats prevent animals from hitting those high metabolic thresholds.

What These Cellular Trade-Offs Mean for Mammal Lifespan

Unlike many birds and cold-blooded animals that maintain telomerase activity throughout life, most large mammals shut down somatic telomerase shortly after development to prevent tumors. This biological constraint leaves mammals particularly vulnerable to early-life telomere loss because they cannot easily repair or lengthen chromosomes later on. The study underscores that population context and individual sex must be factored into evolutionary biology models, as overlooking these variables can completely obscure how early development shapes aging in the wild.

The research was published in Philosophical transactions of the Royal Society of London. Series B, Biological sciences on November 12, 2026.