Research: Testosterone-driven aggression may be a key part of cooperative evolution in meerkat populations

In a study published this week in the journal Nature Communications, a research team led by Christine Drea, professor of evolutionary anthropology at Duke University, showed that testosterone-driven aggression may be a cooperative evolution in the meerkat population pivotal parts.

The meerkat population has a clear “ruler”: the female leader. Together with its partner, it rules a group of subordinate females and male meerkats of all ages. According to these new results, its “dominance” almost entirely depends on its very high testosterone levels.

“Subordinates” help raise the cubs of the female leader. They cannot raise offspring by themselves. The leading spouse needs the help of the group to find food and protect their cubs, while they are busy finding food for themselves.

However, the female leader is not a completely benevolent leader. In order to ensure that “subordinates” pay full attention to its cubs, it will often attack pregnant “subordinates”, drive them out of the population, or kill their newly born cubs.

Therefore, in any given year, few adult “subordinate” females in a population can give birth to surviving cubs. On the other hand, a successful female leader can have as many as three or four cubs in a good year.

In addition to preventing “subordinate” female animals from reproducing, the female leader also rules by pushing, biting, and roaring, marking her own territory by rubbing rocks and bushes, and spreading the irritation produced by the glands hidden under her tail. Odor marker substances.

Now, researchers have discovered that the “dominance” of the female leader, and the success of it, is due to very high testosterone levels.

Drea said: “We always think that male competition is driven by testosterone, but here we show that it is also driving female competition.”

To test the relationship between testosterone levels and the success of female leaders, the research team studied 22 meerkat populations in the Kuruman River Reserve in the Kalahari Desert in South Africa.

These meerkats have been studied for decades and have become accustomed to the existence of humans. This allows researchers to study the behavior of female meerkats throughout pregnancy – note all the time they exhibit aggressive behavior – and collect blood and feces to measure their testosterone levels.

“In the non-pregnant female meerkats, the testosterone levels are equivalent to the males, but slightly lower in the subordinate females. But when the female leader becomes pregnant, their testosterone levels will rise.” Drea said.

As the pregnancy progresses, the female meerkat’s aggressiveness and testosterone levels increase. Their cubs are also very aggressive after birth.

But is testosterone actually driving all these aggressiveness? To answer this question, the researchers treated some female meerkats with flutamide, which is a testosterone receptor blocker that prevents the effects of testosterone in the body.

The female meerkats treated with flutamide did not push, bite, or growl like before. They also don’t mark their territories as often as before. The subordinates discovered this and were no longer so respectful. Their leader has lost its advantage.

The descendants of the leader also lost their advantage. Without the stimulation of testosterone, their behavior has also changed. The cubs treated with flutamide were calmer and less aggressive towards subordinates.

Drea said: “Subordinate females and their cubs are also aggressive, but not as many as the female leader and their cubs. It is this difference that gives the female leader an advantage, and it is this difference that we use testosterone. The blocking agent is completely eliminated.”

The intergenerational effect of hormones means that testosterone does not just help female leaders have more pups. It also helps her cubs get a good start in life by bullying their subordinates.

Drea said: “Here, our experimental results reveal a new mechanism of cooperative reproduction evolution. This mechanism is based on testosterone-mediated attack and competition between females.”

“Female animals are not primarily competing for food. The competition is to ensure that other individuals help raise their cubs. And testosterone helps them win this reproductive battle.”

Researchers say that the aggression evoked by the female leader’s testosterone is the “glue” that holds the cooperating group together. If females are treated with testosterone blockers for longer, they expect that the “maternal society” will be overthrown and the structure of the group will be temporarily unstable.

“When people think of cooperation, they usually think of altruism or helping others,” Drea said. “This research shows that cooperation can also be produced through offensive means, and it is quite effective.”