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Impact of Early Life Adversity on Marmot Longevity Revealed

Early-life adversity can lead to lasting health repercussions, a reality that applies not only to humans but also to wildlife. Researchers have developed a Cumulative Adversity Index (CAI) that allows for the quantification of various hardships, such as poverty and stress, which can inform strategies for improving health and longevity. This concept has generally been focused on human populations but has potential applications in wildlife conservation.

Despite some research into the effects of early stressors on animals, comprehensive analysis has been limited by a lack of long-term data. However, a groundbreaking study by biologists at UCLA aims to change that by establishing the first CAI for yellow-bellied marmots, based on an impressive 62 years of data collected at the Rocky Mountain Biological Laboratory in Colorado. This research stands out as one of the longest ongoing studies of individually marked mammal populations in the world.

The findings of this study, published in Ecology Letters, outline a systematic approach that can be utilized by other researchers with extensive datasets on various species to craft their CAIs.

The researchers identified both anticipated and unexpected stressors affecting marmot survival and longevity. While it was expected that a delayed onset of the growing season would harm survival rates—due to the necessity for marmots to accumulate weight for their prolonged hibernation—surprisingly, summer drought had no discernible negative effect. Additionally, predation risks were found to be less impactful than initially assumed.

One of the most significant findings was the effect of maternal loss, which adversely impacted pups’ survival rates even post-weaning, likely because young marmots often remain dependent on their mothers for up to a year.

Doctoral student Xochitl Ortiz-Ross led the analysis by focusing on female marmots born after 2001, which marked the start of stress quantification. This method provided a reliable record of genetic backgrounds, ages, and lived experiences of the marmots until 2019. Due to their behavior, females tend to remain close to their birthplace, allowing researchers to monitor them throughout their lives.

The marmot population studied spans a significant elevation gradient of approximately 984 feet (300 meters), leading to distinct environmental and demographic conditions for the up-valley and down-valley groups. Bi-weekly trapping sessions from spring through late summer enabled researchers to gather essential data on the marmots’ behavior, morphology, and physiology.

Ortiz-Ross considered various measures of adversity that could influence a pup’s chance of survival during its first year, such as late seasonal start, drought conditions, predation pressures, and maternal health factors. These variables were analyzed using computer modeling, assessing the impact of standard, mild, moderate, and acute adversity levels on survival probabilities. The analyses revealed that both moderate and acute adverse conditions drastically decreased survival chances, by 30% and 40% respectively.

Interestingly, while survival odds were generally higher in the up-valley population, the consequences of maternal loss significantly diminished survival chances across all models, showcasing a decrease of up to 64% under moderate adversity conditions. Additionally, the model identified that poor maternal mass and late weaning further impeded survival, but drought conditions surprisingly appeared to enhance survival odds in most scenarios, except for scenarios classified as acute adversity.

The average lifespan of adult marmots was found to be around 3.8 years, with acute adversity leading to a threefold increase in risk regarding life expectancy impacts. Ortiz-Ross noted, “The CAI effectively measures short-term survival risks in yellow-bellied marmots. Our findings indicate that negative experiences in early life can diminish adult lifespan, and positive experiences do not negate these early adversities.” This underscores the cumulative nature of adversity in marmots.

The research supports the notion that a CAI can serve as an impactful tool in evaluating how multiple stressors experienced early in life affect long-term survival among yellow-bellied marmots.

Co-author Daniel Blumstein, a professor of ecology and evolutionary biology, emphasized the importance of understanding the intersection of various stressors affecting biodiversity management. “We typically examine individual factors in isolation—like human interactions, predation, or climate impacts,” he stated. “However, these elements often coexist and combine to create cumulative effects, demonstrating the need for a comprehensive approach in conservation strategies.”

This research suggests that conservation tactics for marmot populations may benefit from focusing on down-valley groups, which face challenges related to maternal health, while identifying that factors like predation and drought are not as pressing as initially believed.

More information:
Xochitl Ortiz-Ross et al. Cumulative adversity and survival in the wild. Ecology Letters (2024) DOI: 10.1111/ele.14485

Source
phys.org