Biologists have found that early life adversity can also affect the health and lifespan of marmots.

Exposure to adversity early in life can have permanent effects on health, even if circumstances improve dramatically later on. Scientists use the Cumulative Adversity Index (CAI), which quantifies hardships such as poverty and stress, to understand an individual’s health and longevity over their lifetime. This helps governments, health care providers and families identify concrete measures they can take to improve people’s lives.

Wild animals can also encounter adversity early in life, but the impact this has on survival and lifespan is unknown. Similar tools could help scientists protect animal populations by identifying and mitigating the stressors that affect them most, but few populations have been studied long enough to provide the data needed to develop such CAIs.

UCLA biologists are hoping to change that by creating the first-ever cumulative adversity index for yellow-streaked marmots, based on 62 years of continuously collected data at the Rocky Mountain Biological Laboratory in Colorado — the second-longest study of an individually tagged mammal in the world.

The study, published in the journal Ecology Letters, provides detailed instructions for scientists with large datasets for other species to create their own CAIs.

The index they developed identified predictable but unexpected stressors that had significant effects on marmot survival and longevity. For example, marmots need to gain weight over the summer for their seven to eight months of hibernation, so it is not surprising that a delayed start to the growing season would reduce survival. However, the lack of effect of summer drought was unexpected. Predation also played a smaller role than expected.

It’s not surprising that the death of the mother played a large role, but it still played a large role when it occurred after the puppies were weaned. This may be because puppies stay with their mother for a full year after weaning.

To create the index, doctoral student Xochitl Ortiz Roth selected data from female marmots born after 2001, when the researchers began quantifying physiological stress, and that had remained in one of the studied colonies until 2019, ensuring an accurate record of lineage, age and lifetime experiences. While males typically disperse, females remain in the area where they were born, allowing biologists to observe them throughout their lives.

The marmots span an elevation difference of 984 feet (300 meters), with upper and lower valley groups experiencing different environmental and population conditions. Scientists capture members of the group every two weeks during the marmots’ active season from spring through late summer to collect data on their behavior, morphology and physiology.

Ortiz-Ross identified delayed start of season, summer drought, predation pressure, large numbers of pups, male-biased pups, late weaning, underweight maternal bodies, high maternal stress, and maternal loss as indicators of ecological, demographic, and maternal adversity that may affect whether pups survive their first year of life. She wanted to see if these factors had any effect on the length of time individuals lived after the first year of life.

These variables were entered into computer models quantifying standard, mild, moderate and acute adversity. All models yielded similar results: moderate and acute cumulative adversity reduced a pup’s chances of survival by 30% and 40%, respectively.

Pup survival odds increased significantly towards the trough in all models, but maternal loss reduced survival odds in all models, decreasing them by up to 64% in the moderate adversity model, maternal underweight reduced chances of survival by 77% only in the moderate adversity model, and delayed weaning reduced survival odds by 33% only in the standardized and raw models.

Surprisingly, drought increased the odds of survival in all adversity models except the acute adversity model, with the largest effect seen in the moderate adversity model.

Although the average adult life expectancy is 3.8 years, acute CAI increased the risk of adverse life expectancy outcomes threefold.

“We found that CAI effectively reduced short-term survival risks in yellow-legged marmots, and that in the long term, increased early-life adversity reduced adult lifespan,” Ortiz-Ross said. “Positive effects did not counteract early adversity, suggesting that adversity accumulates in marmots and cannot be fully reversed by positive experiences.”

Results supported the hypothesis that the CAI could be a useful tool to assess the effects of multiple early-life stressors on long-term survival in yellow-legged marmots.

“What we’re facing when it comes to managing biodiversity is death by a thousand cuts. We typically study one component at a time — humans, predators, climate –” said co-author Daniel Blumstein, a professor of ecology and evolutionary biology.

“But these effects occur simultaneously and have cumulative effects. We need a way to work out which of these stressors, or which combinations, have the greatest cumulative impact. Our study shows that CAI can do that for marmots.”

For example, a conservation plan for this marmot population might target downstream groups that surprisingly performed a little worse in reducing maternal mortality and improving maternal fitness, but might not need to target reducing predation or countering the effects of summer drought, which may not be as important as expected.