The incredible shrinking and growing brains of Indian jumping ants

New research on ants has shown a first in insects: the ability to shrink and then regrow their brains in a big way.

It relates to how these particular ants, called Harpegnathos saltator, or the Indian jumping ant, reproduce.

"In most ants, the queen is the only member of the colony that lays eggs," says Clint Penick, an assistant professor of biology at Kennesaw State University in Georgia. "The workers just do all of the hunting and take care of the babies and all of the chores in the colony. But the queen is the only one who reproduces. And when she dies, the colony dies."

Not so for this type of ant, native to India. Their worker ants have the ability to mate and reproduce. So when the Indian jumping ant queen dies, "it actually triggers a dominance tournament. And they'll fight each other over a month to decide who's going to be the next ant to replace the queen."

(These are all females we're talking about. The males really aren't involved in anything here except mating and dying.)

The queen doesn't have an exact replacement. A handful of tournament winners — called "gamergates" — all assume queen-like duties of laying eggs.

Penick and his colleagues found that when the ants take on the role of gamergate, their brains shrink by 19 percent on average. The shrinkage likely happens so that they can save energy to focus on producing eggs. Hormones trigger additional changes in the ants, including larger ovaries, less venom production and much longer lifespans.

The fact that the ants' brains shrink to reproduce wasn't new.

"But what we didn't know was if they had the capacity to regrow them back to their previous size," Penick tells NPR's Lulu Garcia-Navarro on Weekend Edition. "The typical wisdom is that once you lose brain cells, they don't come back."

Penick and other scientists plucked these gamergates away from their colonies for a few weeks. The thinking was that the lack of social interaction and care would make them revert back to their previous worker status.

It worked. After several weeks, the ex-gamergates were back to being lowly workers — with their bigger brains regrown.

"When we started the study, we didn't know if any insect was actually capable of this," Penick says.

"We are now starting to find that there are animal species that are capable of shrinking their brain and then regrowing them, even humans to some degree, but not nearly on the scale to what we see here."

Still, there are potential implications for humans.

"It tells us that brains are a lot more plastic and have a lot more abilities to change back and forth between their size than we knew," Penick says. "And ants, their brains have some shared traits with humans, believe it or not. So now we're looking at digging into some of the genetic and other neural mechanisms that are underlying these brain changes."

Penick and his co-authors' study is published in Proceedings of the Royal Society B.

Peter Breslow and D. Parvaz produced and edited the audio interview.

Copyright 2021 NPR. To see more, visit https://www.npr.org.

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