Stressed-out monkeys show it in their genes

A new study demonstrates a link between social class and genetics in non-human primates.

AP Photo/Rajesh Kumar Singh
In this image a Rhesus macaque monkey holds a Bharatiya Janata Party or BJP flag in Faizabad, India.

Stressed-out monkeys tend to have a lower quality of life. But why? It turns out the answer might be in their genes.

Rhesus monkeys have a clear social ranking system. Those in the highest ranking group have the best access to food, water, and grooming. The opposite is also true: those in the lowest group have a difficult time when resources are scarce.

Researchers began with 49 captive female rhesus macaques of medium social rank. They sorted the monkeys into ten new groups, so that the monkeys sorted themselves into diverse social classes. Afterward, the scientists collected blood samples from the animals.

Blood samples showed a significant relationship between gene expression and social rank. So much so that, 80 percent of the time, the researchers were able to predict an individual monkey's social status just by looking at its genes.

Notably, it appeared that genes associated with the immune system were more active among low-ranking group members. This immune system activity could be tiring for the animals over time.

On the positive side, immune system activity levels did not seem fixed. As the researchers added new group members, altering the social stratification, gene expression changed. As the monkeys moved up in the world, they became less stressed.

This finding demonstrates an important linkage between the social world and individual physiology.

“If an individual is able to improve their social environment, the genome is pretty plastic, which is kind of optimistic,” Jenny Tung a geneticist at Duke University and the study's lead author told The New York Times.

In future studies, Tung plans to explore the question of the health impacts of social rank-associated gene expression.

This study appears in this week's Proceedings of the National Academy of Sciences.

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