Why meerkat mobs are crucial to the survival of the species

By Georgia Lambert via SWNS

Testosterone-fuelled violence drives female meerkat mobs - and is crucial to the evolution of the species, reveals new research.

Meerkat societies have a clear boss - the matriarch, who rules over a group of subordinate males and females of all ages with her lucky mate.

The cat-like carnivores work together in groups to hunt and they rely on one another to help raise the matriarch's pups.

But according to researchers at Duke University, the matriarchs aren't considerate and kind-hearted leaders.

To ensure her pups are given undivided attention, the matriarch will make a beeline for other pregnant meerkats, expelling them from the group, or killing the newborns.

This means that while only a handful of pups survive the wrath of the matriarchy, a successful leader could have as many as three or four litters in a good breeding year.

As well as preventing the subordinate females from reproducing, the matriarchs dominate their societies by pushing, shoving, biting, and growling at others who get in their way.

This bullish behaviour continues when they mark their turf by rubbing their bums against rocks and shrubs to spread a pungent scent-marking substance produced in glands hidden under their tail.

To understand what drives the dark side of their leaders, the team of researchers, led by Professor Christine Drea, observed a mob of meerkats and found that the matriarch's dominion is caused by very high levels of testosterone.

Professor Drea, who teaches Evolutionary Anthropology at the university in North Carolina, said: “We always think of male competition being driven by testosterone, but here we’re showing that it’s driving female competition too."

To test how testosterone levels related to the matriarch's success, the team worked on 22 meerkat mobs at the Kuruman River Reserve in South Africa's Kalahari Desert.

The meerkats, who have been subjected to research for decades, are now used to having humans around, which allowed the team to study the matriarch's behaviour throughout their pregnancies.

Over the course of their terms, the team was able to monitor any aggressive behaviours, while collecting samples of blood and faeces to measure the levels of testosterone in their bodies.

Professor Drea said: "In non-pregnant matriarchs, testosterone values are equivalent to the males,' and just a little bit lower in subordinate females.

"But when matriarchs get pregnant, they ramp up."

Professor Drea went on to explain that both the matriarch's aggressiveness paired with their testosterone levels increased together as their pregnancies progressed.

After giving birth, their pups were born aggressive and the team watched as they furiously demanded care and feeding from the subordinates like "spoiled little brats."

To find out whether testosterone was responsible for this aggressiveness, the team treated some of the matriarchs with flutamide - a testosterone-receptor blocker that shuts off testosterone's hormonal actions in the body.

And just like the team expected, the matriarchs who were treated with flutamide didn't shove, bite, growl, or mark their territory as much.

The subordinates observed these changes and as their boss lost her edge, they stopped being respectful of their leader.

Alongside their mom, the pups also lost their edge and without the testosterone pumping through their bodies, they became calmer and less aggressive towards those from lower ranks.

Professor Drea commented: "The subordinate females and their pups are also aggressive, but not as much as the matriarchs and their pups.

“It's this difference that gives matriarchs their edge, and it's this difference that we completely erased with testosterone blockers.”

This study, which showed the degradation of a whole society once aggression was taken away, demonstrated that the cross-generational effect of hormones not only helps the matriarch give birth to more pups but also springboards them into life by bullying the lesser-important meerkats.

And while blocking the matriarch's testosterone changes the pup behaviour, the hormones may be sustaining a cooperative family dynasty.

Professor Drea said: "Here we have experimental results revealing a new mechanism for the evolution of cooperative breeding.

"One that is based on testosterone-mediated aggression and competition between females.”

“Females are not primarily competing for food.

"Competition is about ensuring that other individuals help raise their kids. And testosterone helps them win that reproductive battle.”

The researchers explained that the matriarch’s testosterone-fueled aggression is the "glue that holds the cooperative group together."

What's more, if the female leaders continued to be treated with testosterone blockers, it is expected that the matriarch would be overthrown, and the group’s structure would be temporarily destabilised.

Professor Drea said: "When people think about cooperation, they usually think about altruism or helping others.

“This study is showing that cooperation can also arise through aggressive means, and quite effectively.”

The findings were published in the journal Nature Communications.