Early-life trauma and struggles can literally get under the skin of young red squirrels in the Yukon, affecting their long-term survival a new study shows.
Life in the Yukon can be tough for young red squirrels. Frigid winters, food scarcity, intense competition for territories, and the threat of becoming prey to large predators like the Canada lynx are just some of the trials they face.
Scientists want to know what factors, if any, can buffer young squirrels against these threats.
Lauren Petrullo, assistant professor in the ecology and evolutionary biology department at the University of Arizona is part of the Kluane Red Squirrel Project, a multi-university long-term field project that has tracked and studied thousands of wild North American red squirrels in the southwestern part of Canada’s Yukon territory for over 30 years.
A new study published in the journal Proceedings of the Royal Society B: Biological Sciences which Petrullo led with David Delaney, a postdoctoral fellow at the University of Colorado Boulder, finds that the more challenges young squirrels face in the year they are born, the shorter their adult lifespan.
Red squirrels who make it past their first year of life live about 3 1/2 years, on average, but early life adversity can cut life expectancy by at least 14%.
But there’s a big caveat.
“The ecosystem red squirrels inhabit in this region is unique,” Petrullo says. “Every three to seven years, their favorite food—seed from cones of white spruce trees—is produced in superabundance during what we call a food boom.
“We found that these booms, even though rare, can interrupt the biological embedding of early-life adversity. If a squirrel had a harsh first year of life, if they were lucky enough to experience a food boom in their second year of life, they lived just as long—if not longer—in spite of early-life adversity.”
The team replicated a food boom by offering wild squirrels in the Yukon peanut butter as a supplemental food source. The peanut butter didn’t have the same effect as the naturally occurring food boom did.
“This suggests that the buffering effect we see is not really just about an increase in available calories,” Petrullo says. “It’s probably about shifts in larger population-level dynamics, like competition.”
Petrullo and her colleagues are eager to tease out the mechanisms that link squirrels’ early developmental conditions with later-life survival. What they learn could inform scientific understanding of human resilience, too.
“Our findings in red squirrels echo what we know about how early-life adversity can shorten adult lifespan in humans and other primates,” Petrullo says. “Humans vary widely in how vulnerable or resilient they are to challenges faced during early development.
“Our study demonstrates that future environmental quality might be an important factor that can explain why some individuals appear to be more, or less, susceptible to the consequences of early-life adversity.”
While it might be surprising that scientists can glean insights about human resilience from wild red squirrels, Petrullo points out that squirrels are rodents, and rodents are commonly used as models for humans in laboratory settings.
“Many lab experiments have limited relevance for broader dynamics between ecology and evolution, because it can be hard to really replicate the ecological challenges that animals have evolved to cope with in a lab setting,” she says.
Wild red squirrels, on the other hand, allow for such investigations and are an especially useful study group for questions regarding the early-life environment, Petrullo says. Although growing up as a young squirrel in the Yukon can be difficult, with lots of things making early development challenging, there are also things that can go right.
“Some red squirrels have the luck of being born into gentler early environments, akin to being born with a silver spoon,” Petrullo says. “Because of this, we’ve got this really nice individual variation in early-life environmental quality across a natural ecological environment.”
This environment, however, is expected to experience a great deal of change as global temperatures continue to rise.
“As food boom patterns begin to change,” Petrullo says, “the pathways that connect early-life experiences and lifespan may change as well, potentially offering important insight into how animals may adapt to increasingly challenging environments.”
Additional coauthors are from the University of Alberta, the University of Michigan, the University of Colorado Boulder, and the University of Saskatchewan.
Source: University of Arizona
