Red squirrels that live in Canada's Yukon Territory can lead quite a tough life. Bitterly cold winters, scarcity of resources, intense competition for habitat, threats from large predators such as the Canada lynx, and even take great reproductive risks due to their genetic fitness. All these stressors take their toll on these resilient rodents. Their early life struggles can also leave a lasting mark. The more challenges young red squirrels encounter in the year they are born, the shorter their adult lives. The findings are detailed in a study published April 24 in the journal Proceedings of the Royal Society B: Biological Sciences and may have some consequences for humans.
Food flourishes
Red squirrels are about 11 inches long and weighs just over half a pound average. They are known for their rust-colored coat and “sweary babble” above the trees. The new study uses data collected by the Kluane Red Squirrel Project, a multi-university long-term field study. The project has tracked and studied thousands of wild North American red squirrels in the southwestern region of the Yukon for more than thirty years, individually tagging and tracking individual red squirrels to learn how they cope with whatever is thrown at them.
The new study Analyzing the observations revealed that red squirrels that survive the first year live an average of about 3.5 years. However, early life adversities such as food scarcity can shorten their life expectancy by at least 14 percent.
[Related: A Medieval strain of leprosy is infecting squirrels in the UK.]
“The red squirrel ecosystem in this region is unique,” study co-author and University of Arizona ecologist and evolutionary biologist Lauren Petrullo. said in a statement. “Every three to seven years, their favorite food – seed from white spruce cones – is produced in abundance during what we call a food boom.”
The team found that while these food booms are rare, they can interrupt some of the squirrels' biological processes and help shape their lifespans.
“If a squirrel had a difficult first year of life, if it was lucky enough to experience a food boom in its second year of life, it lived just as long – if not longer – despite the setbacks in its early life,” says Petrullo. .
Rodents as proxies
Rodents such as squirrels, rice and mats are often used as models for humans in a laboratory setting. However, the laboratory environment often has limited relevance to the bigger pictures of what is going on at the ecological and evolutionary level.
“It can be difficult to truly replicate the ecological challenges that animals have evolved to meet in a laboratory environment,” says Petrullo.
Wild red squirrels may offer scientists an opportunity to better study the role the environment plays in early life. Petrullo and her colleagues hope that continued observations in the wild can help them learn more about the biological mechanisms that link squirrels' early developmental conditions to their later-life survival. This could provide some insight into our understanding of human resilience.
[Related: Nature wasn’t healing: What really happened with wildlife during pandemic lockdowns.]
“Our findings in red squirrels reflect what we know about how early life adversity can shorten adult lifespans in humans and other primates,” Petrullo said. “People vary widely in how vulnerable or resilient they are to challenges during early development. Our study shows that future environmental quality may be an important factor explaining why some individuals appear to be more or less susceptible to the effects of adversity in early life.”
'Born with a silver spoon'
Although raising a young red squirrel in the Yukon can be quite difficult, there are some things that can go right.
“Some red squirrels are fortunate to be born in gentler early environments, akin to being born with a silver spoon,” Petrullo said. “This gives us a very nice individual variation in the environmental quality of early life in a natural ecological environment.”
However, as global temperatures continue to rise, much is expected to change in this environment. It is possible that food boom and other ecological patterns could change along with climate, and the connections between early life experiences and lifespan could also change. According to Petrullo, these changes could provide more insight into how animals can continue to adapt to environments that only make it harder to survive. Future research could also help scientists learn more about what environmental factors may protect these squirrels from ongoing environmental threats.
