Study with the rhesus monkeys of Cayo Santiago offers clues about how humans are affected by adversity

After the destruction left by the hurricane maria In Puerto Rico, the rhesus macaques, apes of Indian origin that live freely in Cayo Santiago, in Humacao, they overcame the hurdles left by the natural disaster, they were more tolerant, even with their old rivals, in addition to seeking new social relationships – a behavior very similar to that of humans in these circumstances. However, it has also been found that those that survived showed molecular ageing.

This is what emerges from two studies carried out in the Caribbean Primate Research Center, of the Medical Sciences Campus (RCM)of the University of Puerto Rico (UPR)an entity that has a reciprocal agreement with local and international scientists to develop research that, for the most part, is behavioral, since it is “the only place in the world where psychological methods and observation of social behavior can be used, with genetic techniques, in such a large group of monkeys,” according to the abstract of one of the studies.

Marina Watowich is the principal investigator of the study
Marina Watowich is the principal investigator of the study “Natural disaster and immunological aging in a non-human primate”-published in the scientific journal Proceedings of the National Academy of Sciences (PNAS). (Supplied)

In fact, in the investigation “Natural disaster and immunological aging in a non-human primate”-published in scientific journal Proceedings of the National Academy of Sciences (PNAS) – it was found that the rhesus macaques that survived the hurricane maria they showed a molecular aging of an average of two years, greater than animals that had not suffered the storm – approximately seven to eight of the human life.

The findings suggest that experiencing an extreme hurricane is associated with alterations in the regulation of immune cell genes similar to aging.

Camille Testard of the University of Pennsylvania, lead author of research on social connections among monkeys after the hurricane.
Camille Testard of the University of Pennsylvania, lead author of research on social connections among monkeys after the hurricane. (Supplied)

“Individuals who experienced the hurricane had immune cell gene expression profiles that were more similar to immune cell gene expression in older individuals,” the study’s principal investigator explains in an email. Marina Watowich, from the Department of Biology, University of Washington.

The scientist makes the caveat that they do not study humans, but she does point out that rhesus macaques have a physiology and an immune system very similar to us “and are frequently studied to obtain information on human biology.” In that sense, she affirms, it has been proven that People who have survived extreme hurricanes and other natural disasters are at increased risk of cardiovascular disease and other conditions typical of older populations.

“All of this suggests that the experience of extreme natural disasters can accelerate immune aging, which could lead to an earlier onset of age-associated diseases,” says Watowich.

Meanwhile, researchers from the University of Pennsylvania, along with other research centers in the United States, have also managed to link the complexity of the social life of a group of living primates with a very human strategy: “The ability to unite in the face of a catastrophe naturally and in this way broaden support and have a broader social network with new friends”, indicates scientist Camille Testardof the University of Pennsylvania, who was in charge of research on the social connections between these monkeys after the passage of the hurricane.

“Surprisingly, most of the resident macaques survived Hurricane Maria. This allowed us to investigate how groups of rhesus macaques, which are primates like us, respond to a drastic change in their environment. In Cayo Santiago the monkeys have been studied for a long time, so we were able to compare their social behavior before and after the hurricane”adds Testard.

“These results speak to the impressive social flexibility that rhesus macaques are capable of. When things get difficult, with fewer resources, the macaques decide to invest in their social relationships instead of becoming more aggressive and competitive,” says the researcher, who believes that these discoveries can also help us understand people and how they cope. to extreme situations.

“Overall, rhesus macaques have long served as a model for human health and social behavior, as they share many similarities with humans in several domains,” he says. researcher Alyssa M. Arre, scientific director of the Cayo Santiago Biological Station.

genetic similarities

As Arre explains, rhesus macaques and humans share a great genetic similarity, similar immune systems and even aspects of their social behavior and cognition.

“Because of their interdisciplinary nature and the way different elements of neurobiology, such as social behavior and development, are linked, studies of this nature can help improve our understanding of how sociability affects the brain and also have potential implications. for neurobiological disorders”, adds Arre, indicating that in recent years, several works have investigated how the health, sociability, demography and genes of monkeys have been affected by the stress of the natural catastrophe and the period subsequent ecological and social instability.

For Arre, Cayo Santiago is unique and as a “natural laboratory” it allows scientists to study monkeys that live in a natural environment, where they roam freely and can interact “with other groups of monkeys to perform social behaviors such as grooming, fighting and play”.

“Thus, their social behaviours, the relationships they establish with other monkeys and their interactions with other groups and their environment reflect real life and provide a more solid population for researchers looking for a comparative model for their research”, says Arre.

In fact, the researchers believe that these findings help answer a big pending question about the benefits of social relationships. In addition to that they have possible implications for human behavior, in particular for understanding disorders related to neurological development.

In an article published in the “Penn Today” newsletter (from the University of Pennsylvania) entitled “Social connections influence brain structure in rhesus macaques,” Professor Michael Platt of the Penn Integrates Knowledge Professorships explains that previous research on human social networks have hinted at that relationship. “The literature, for example, relates the variation in the size of the amygdala (in humans) to the number of Facebook friends you have. But it’s hard to get granular (detailed) data on human social interactions because we can’t follow people around the clock.”

In the work, published in Science Advances, researchers from the University of Pennsylvania found that for these nonhuman primates the number of social connections predicted the size of key nodes in parts of the brain responsible for social decision-making and empathy. . Specifically, they determined that for macaques with more grooming partners, the medial superior temporal sulcus (STS) and ventral dysgranular insula (in the brain) became larger.

“For the first time, we can relate the complexity of the social life of a group of living primates to the structure of the brain”, Testard explains, although he indicates that, because five years have passed since the hurricane and the vegetation in Cayo Santiago has not yet fully recovered, now it is being investigated whether the monkeys continue to be more socially tolerant and less aggressive. “We are also interested in the resilience that social relationships can provide in the face of a drastic and lasting change in the ecosystem,” adds the researcher, while inviting us to pay attention to a new study on this subject that will be published soon.

“There’s something about the skills it takes to make and keep friendships that you get from parents. You’d think you’d be born with it, but it seems more likely to come from the patterns and interactions you have,” explains Dr. Platt in the “Penn Today” post. “Perhaps that means that if your mother is outgoing and you have the ability to be outgoing, your brain can mature in a way similar to the findings we’ve discovered. That’s intriguing.”

Similarly, although all of these findings relate specifically to rhesus macaques in the wild, they have potential implications for human behavior, particularly for understanding neurodevelopmental disorders such as autism.

We expected that the monkeys would use their closest allies to deal with the ecological devastation of the hurricane and that they would invest in their existing relationships. Instead, the macaques expanded their social networks and increased the number of individuals with whom they tolerated sharing limited resources, such as shaded space in which to sit,” explains the study abstract.

According to these results, the observed specimens had forged new relationships after the storm, such as with unknown or unfamiliar monkeys, “a pattern observed in humans after catastrophic events that affect entire populations,” the study highlights, to also underline that “This peculiarity resulted in a more tolerant society as a whole.”

For the researchers, this finding represents “strong evidence of the flexibility in the ability of rhesus macaques to negotiate their social landscape after a natural disaster”, they expose in the work. But, because it is unknown what long-term effects this behavior may have on life expectancy or offspring, “the authors believe the findings may help people understand how we cope in the midst of natural disasters.” .

In detail

-The Caribbean Primate Research Center is an important research space at the UPR worldwide with a population of rhesus monkeys, of the Macaca mulatta species, that interact freely on the islet of Cayo Santiago, with 38 cuerdas, since 1938.

– Scientist CR Carpenter brought the first 408 monkeys from India because he was concerned that the outbreak of World War II would not allow scientists to travel to the Old World to study primates.

– It is the only place in the world where psychological methods and observation of social behavior can be used, with genetic techniques, in such a large group of monkeys.

– The rhesus macaque is considered the best animal model to study AIDS and other human infections -such as COVID-19-, as well as autism, human behavior, language and genetics, in addition to new vaccines, among other aspects related to diseases that affect to the humans.

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