PREVIEW

A devastating hurricane that hit Puerto Rico in 2017 had an unusual effect on a monkey society - making them more friendly towards each other.
Hurricane Maria hit Puerto Rico in 2017, killing more than 3,000 people. It also destroyed 63% of vegetation on Cayo Santiago (also known as Monkey Island), which is home to a population of rhesus macaques.
Seven years on, tree cover remains far below pre-hurricane levels - making shade from the Sun precious, this close to the equator.
The new study, led by the universities of Pennsylvania and Exeter and published in the journal Science, shows the storm damage altered the habits of the monkeys as it showed the evolutionary benefits of sharing.
Tolerant macaques who accepted pals who could share their shade had a survival advantage over those who fought over territory.
“In response to the drastic changes caused by the hurricane, macaques persistently increased tolerance and decreased aggression towards each other,” said Dr Camille Testard, from the University of Pennsylvania.
“This enabled more macaques to access scarce shade, which is critical for survival.”


Dr Testard added: “We examined 10 years of data on the strength and number of macaques’ social ties, before and after the hurricane.
“Before the hurricane, tolerating others had no impact on risk of death.
“Afterwards, macaques that displayed more than average social tolerance – and were therefore better able to share shade – were 42% less likely to die than those that were less tolerant.”
Social behaviour was assessed by recording aggression and how often individuals were seen sitting together.
“Macaques aren’t the best at sharing resources – be they food or shade. They are well known to live in an aggressive, highly competitive society,” said Professor Lauren Brent, from the University of Exeter.
“But in the heat caused by ecological changes, often around 40C, the macaques had to share space or die.”
Dr Testard said that the behaviour did not just extend to situations in which they are under threat from heat - but made them friendlier in general.
“To access shade, they need to tolerate – and be tolerated by – others, and we found that this tolerance spills over into other daily interactions.
“Macaques that began sharing shade also spend time together in the mornings, before the day’s heat forces them to seek shade.
“In effect, the hurricane changed the rules of the game in the monkeys’ society.”
Professor Brent added: “For group-living animals, social relationships may allow them to cope with disturbances in the environment, including human-induced climate change.
“We were surprised the macaques’ social behaviour was so flexible, making them resilient to this environmental change, but some species may not display this same flexibility.”
The research team included Arizona State University and New York University.
Funders included the National Institutes of Health, the European Research Council, the National Science Foundation and the Royal Society.