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To become queen, these ants fight — then shrink their brains

Female Indian jumping ants that lose their bids for the crown can regrow their brains — a feat that has never been seen before in insects.
Jumping ant (Harpegnathos saltator)
Indian jumping ants (Harpegnathos saltator) are known to shrink and regrow their brains.Courtesy of Clint Penick

Most ant species are born into royalty. But for Indian jumping ants, female workers can fight for the crown.

The catch? The winner becomes queen, but its brain also shrinks.

In a study published Wednesday in the journal Proceedings of the Royal Society B, scientists discovered that Indian jumping ants can shrink and regrow their brains within a few weeks — a feat that has never been seen before in insects and is also incredibly rare in the animal kingdom.

"Indian jumping ants are particularly unique," said Clint Penick, assistant professor biology at Kennesaw State University and one of the study's authors. "They shed a part of their brain mass to conserve energy and push resources from the brain to the ovaries for reproduction."

The Indian jumping ants, also known as Harpegnathos saltator, are inchlong arthropods known for their forceps-like jaws and large black eyes. And as their name suggests, these ants can be found in the forests of India where they hunt and leap several inches in search of prey.

Like many ant colonies, the nest of an Indian jumping ant contains a queen and thousands of workers that clean the royal's eggs, hunt for food and feed the larvae.

But the similarities stop there.

The lifespan of most ant colonies is often dependent on the lifespan of the queen. When an Indian jumping ant queen dies, more than half of the colony's female workers participate in a monthlong "tournament" to vie for a seat at the top, Penick said. Indian jumping ant colonies can have numerous queens.

As hundreds of female workers duel each other, they begin to undergo a physiological change that transforms them into queenlike workers called gamergates — "not the online harassment campaign," he said, referring to a harassment campaign that targeted several women in the video game industry in 2014.

A small group of eight to 10 workers will emerge victorious while the losers will return to their worker duties, Penick said. The victors will then activate their ovaries to take on the previous role of the queen, "essentially an egg-laying factory," according to Penick.

During this period, the ovaries of gamergates will increase five times in size while their brains will shrink up to 25 percent compared to the anatomy of the workers.

"The colony will live on, and essentially at this state, they can theoretically become immortal," he said.

Penick said the Indian jumping ant colonies used in the study were the same ones that were collected in India almost 20 years ago and were the first epigenome for the species sequenced.

At some point, he said, he and the other researchers became interested in determining whether brain shrinkage was reversible and created an experiment to isolate newly formed gamergates from the colony.

He said he expected them to die, but what they discovered was that the Indian jumping ants can regenerate the size of the brains and shrink their ovaries back to the size of workers.

"It was incredible," Penick said. "When we lose brain tissue, we may be able to reproduce some brain cells, but it does not wholly repair itself and grow back to its original state. It's gone forever."

The ants have become a "model of developmental plasticity" that can provide details about "what genes control this phenomenon and what parts of the brain retain the ability to regrow," he said.

Penick added he believes queens can revert back to their original form because the losers of the duel for the crown needed to be able to return to their responsibilities as a worker.

"They need more brain capacity," he said. "Their major job is to leave the colony, sometimes meters away, find food and bring it back to the nest."

"They have to remember how to find their way home."