Hurricane Maria & monkey island, ageing worms, & resilience of mind and gut | Last Week in Science (23 Jun 2024)

The changing face of monkeys on monkey island

Credit: Lauren Brent

Santiago Island, also known as 'Monkey Island' in Puerto Rico, was created as a natural laboratory to study rhesus monkeys. It was established in the 1930s with 50 monkeys brought from India. Since then, their biology and behavior have been studied. The devastation that occurred during Hurricane Maria in 2017 changed the island and also the monkeys.

Hurricane Maria killed 50 monkeys of the 1700 who lived on the island and destroyed 63% of the trees and vegetation of Santiago Island. This left little shade for the monkeys who survived the hurricane. Rhesus monkeys are known to be aggressive, especially when it comes to food, mates, and, in this case, shade. An environment with very little tree cover in the sweltering climate of 40°C presented a challenge to the monkeys.

In a recent study published this week, scientists report that this change in their environment led to a change in the behaviour of the monkeys. They studied 10 years of video recordings, including time from pre- and post-hurricane, of monkeys to assess their behaviour involving aggression and whether they would sit with other monkeys. The monkeys were found to be sharing the shade of trees with other monkeys more often than in the pre-hurricane time. The scientists also found that if a monkey was more tolerant of other monkeys when it came to sharing the tree cover, it had a 42% higher chance of surviving. This particular behavior of 'tolerance' did not affect the survival of a monkey before the hurricane. This study is another example of how much animals can adapt to survive in an environment that challenges them.

What can worms tell us about ageing?

A lot of factors are responsible for deciding how long we live. There exists a large variation in lifespan even amongst individuals who die of natural causes. Is this variation caused by genes that decide how long one lives naturally? Genes do play a role, but surprisingly they can explain only 30% of the variation that we see in the natural lifespan of humans. What are the other factors that decide how long we live, provided the environment is the same? Scientists studied tiny worms - C. elegans - to understand the reason, and they found that the answer lies in randomness.

C. elegans live for 2-3 weeks in a controlled laboratory environment. Some of them have a long life and others short - ranging from 8 to 20 days - even though they are the same at the genetic level and living in the same environment.

To understand the difference in lifespan of worms, scientists grew and tracked thousands of worms throughout their entire lifespan. They studied which genes were on or off by looking at the RNA that forms to decode the DNA sequence of the genes and then guides the formation of proteins, thus known as messenger RNA. There exists a balance of mRNA between germ cells and somatic cells. They found that as the worms age, the mRNA balance between germ cells and somatic cells gets disrupted. The disruption happens faster in worms who have a short life as they age faster.

They also found that 40 genes were responsible for causing the imbalance between germ and somatic cells. When scientists experimentally deleted (or knocked out) one of these genes from the worm, then either their life lengthened or shortened depending on which gene was deleted.

But remember that the worms that they had been studying had all the 40 genes present and none of these were absent, and yet there were differences in their lifespan. The scientists suggest that 'the switching on and off of these genes is happening randomly' in the worms. The lifespan of a worm depends on which of these 40 genes are turned on or off. Would we be able to identify similar genes in humans and tinker with them to slow down aging?

Resilience of mind and gut

Resilience is a trait that helps one cope with stress. We talk about the differences in thoughts, behaviour, and action of individuals who are more resilient. A new study has found that even the gut microbes of people who are resilient are different from those who are less resilient.

One hundred sixteen individuals were divided into high and low resilience categories based on their responses to questions like whether they trust their instincts and whether they feel positive towards changes. They next conducted MRI scans on these individuals and collected their stool samples. The high resilience group was found to be less anxious and able to regulate their emotions well - which we already know. They discovered that the gut microbes of the high resilience group were different from those of the low resilience group. The microbes in the high resilience group indicated a healthy gut wall and low levels of inflammation, while in the low resilience group, the microbes were indicative of a damaged and inflamed gut wall.

This study highlights that treating both the brain and gut for conditions that arise out of stress in individuals who have low resilience is a better strategy.