These ants shrink their brains for motherhood — but can also grow them back

Originally published on April 17, 2021.

Researchers have discovered that a species of ant can regrow lost parts of their brain, an ability believed to be rare in the animal kingdom, and never before seen in insects.

In most species of ants, only the queen can reproduce. However in the Indian jumping ant, when the queen dies, female workers have the ability to take on the reproductive role for the colony. But the promotion from worker to queen comes with a catch: the ant loses up to 25 per cent of its brain volume.

"We had already known that they lose this region of their brain. But what no one had ever really thought to look at was, can they get it back?" ant researcher Clint Penick told Quirks & Quarks host Bob McDonald.

When researchers removed these queen-like ants from the colony, they essentially reverted back to workers, and Penick and his fellow researchers found that the ants were able to regrow the missing parts of their brain.

"If I was a betting man, I'm not sure that I would have taken this bet," he said. "It was pretty amazing to see that their brains came back all the way."

The study was published this month in the journal Proceedings of the Royal Society B.

Battling it out to become the queen

In Indian jumping ant colonies, when the queen dies, within hours the worker ants start competing in gladiatorial tournaments to find a replacement.

"What you start to see happening is workers beating each other in the face with their antennae and they do it back and forth really quickly," said Penick, an assistant professor of biology at Kennesaw State University in Georgia. "They're actually pretty fun to watch."

The attacks don't cause physical harm, but they're physically draining, and can last for several weeks. Penick believes that the ants that can continue to deliver and receive these blows, while still having the resources to activate their ovaries and egg-laying capabilities, prove their abilities as the fittest ants in the colony.

At the end of these tournaments, between five and 10 ants stand victorious, and those become known as gamergates (pronounced gammer-gayt), a Latin term that translates to "worker queen."

Quickly, those gamergates undergo a massive internal transformation to take on their new role.

"If you were to look inside one of these workers, you'd see that the ovaries grow from this tiny little piece of tissue to completely swell up and fill the entire abdomen," said Penick. "They also shut down venom production, so their venom glands shrink. And then one of the most amazing things to me is that their brain shrinks, so they lose up to 25 per cent of their brain size." 

Penick believes the extreme transformation is because if the ants are taking on the reproductive roles, they no longer need the cognitive abilities required to hunt, navigate or even clean themselves. 

"Once these workers win the tournament, they no longer have to to perform any really complex tasks," said Penick. "Their only job is to produce eggs. And for that reason, we think that they're losing this chunk of their brain essentially to take all of the calories they have and then push it into egg laying."

Potential inspiration for repairing human brains

Penick, who has been working with these ants for years, wanted to know if it was possible for a gamergate to regain these lost skills. He took several well-established gamergates that had been in their reproductive role for a year, and placed them in isolation. 

After a month deprived of any social interaction and biological reproductive cues from other ants, they were returned to the colony, where they were treated as, and resumed their roles not as fertile gamergates, but as infertile workers. Later, Penick dissected the ants to see if their brain had gone back to full size — and sure enough, they had. 

"It is surprising to see that even something like an insect, with a brain that's so small, and with a lifespan that's usually relatively short, is actually able to maintain this brain plasticity," said Penick.

Now, he wants to further understand the mechanisms at play that help the ants regrow their brains, to see if there are any lessons that could eventually apply to bigger brains.

"Part of my own interest in this was because of my dad. My dad before I was born had a brain tumour the size of a golf ball, so he had surgery where he had part of his brain removed," he said. "It was always amazing to me that he was able to recover from this surgery.... He basically lives a normal life. 

"I do think it would be really interesting to see if there are applications to help humans repair their brains."

Produced and written by Amanda Buckiewicz.