Female rhesus macaques, shown here, have genes that are affected by the animals' social dominance. Credit: Yerkes National Primate Research Center.

A female's social status affects how her genes turn on and off, and those who rank higher tend to be healthier -- so long as their social status doesn't decline, according to a study of rhesus macaques published in the April 9 Proceedings of the National Academy of Science.The study is the first to use an experimental approach to observe how gene expression patterns across a range of genes correlate with an animal's social dominance. It estimates that gene expression can predict the social status of an individual with 80 percent accuracy. "Our study supports the idea that low social status can be bad for the body. But it hints at the idea that if you improve your social situation, your health improves, too," said the study's lead author Jenny Tung, a visiting assistant professor in Duke University's evolutionary anthropology department.Past research has shown that caste-level and social status can change what genes get turned on and off in insects, fish and honeybees. Scientists also have observed that the social environments of both humans and non-human primates affect their hormone levels and mortality risk, as well as the survival of their offspring.Tung said scientists have more work to do to understand how improving social status affects the way genes turn on and off. But she found it "exciting" and "comforting" that her team observed positive changes in the expression of immune-system genes of several monkeys whose social rank increased, she said.The team looked at gene regulation in 49 female rhesus macaques kept at the Yerkes National Primate Research Center at Emory University in Atlanta. The monkeys have a hierarchical rank based on the group in which they live. Males enter new social groups at adolescence to establish their rank order, while females never leave their birth group and take on a rank similar to their mothers' status.To test how gene expression would differ when a monkey's rank changed, the scientists at Yerkes took the female macaques from their native groups and constructed 10 new social units, where rank was determined based on how early a female was added to her unit. Tung and her collaborators then took blood samples from the monkeys and isolated the white blood cells. The results show that lower-ranking monkeys had lower levels of a certain kind of T cell and showed signs of exposure to chronic stress, two findings that helped explain why their genes turned on and off differently than high-ranking monkeys. Her team also looked for changes in the monkeys' DNA and found an animal's rank in dominance correlated with the presence or absence of methyl groups, which help control the switching on and off of genes. The females' immune systems responded rapidly when they moved from a lower social rank to a higher one, to the point where formerly low-ranking animals looked genetically like high-ranking ones. The research was done in collaboration with Emory's primate center when Tung was a post-doc in the Gilad lab at the University of Chicago."We're seeing that there are a lot of effects of social status on genes, including our own, but we are also seeing that many of the changes aren't permanent and that leads to more questions about how you regulate stress," Tung said. This study is "just the tip of the iceberg" when it comes to understanding the relationship between genomics and social environments, she said.University of Chicago is the lead institution on the paper. The study was funded by grants from the National Institutes of Health.Citation: "Social environment is associated with gene regulatory variation in the rhesus macaque immune system." J. Tung, L. Barreiro, Z. Johnson. et. al. April 9, 2012. PNAS Early Edition. pp. 1-6. DOI: 10.1073/pnas.1202734109