This Ant Can Shrink and Regrow Its Brain

Indian jumping ants shrink their brains when they become their colony’s queen, but they can also grow the brain back if they quit the gig

 Indian jumping ant (Harpegnathos saltator)
The Indian jumping ant (Harpegnathos saltator). Clint Penick

In most species of ants, the colony only has one queen and royal status is conferred at birth. But Indian jumping ants (Harpegnathos saltator) offer members of a colony’s sterile, submissive worker caste a chance at a twisted fairy tale.

Among these ants, if the queen meets an untimely end, there is a fleeting chance for a few of the plebeians to make a sudden Cinderella-like ascension to royalty. To change their fate, the workers must win a series of jousting matches against rivals using their antenna to parry and jab at the competition.

When the battle, which can last up to 40 days, concludes, a handful of the most successful combatants begin growing huge functional ovaries that will allow them to begin laying eggs. The bizarre catch is the winning ants also lose nearly a fifth of their brain mass on their way to becoming pseudo-queens.

But new research finds that, incredibly, if the cloistered, egg-laying life of ant royalty doesn’t work out, the pseudo-queens can revert to the lives of commoners and regrow that lost brain tissue, reports Annie Roth for the New York Times. The research, published this week in the journal the Proceedings of the Royal Society B, is the first known instance of an insect losing and regaining brain size.

“Traditionally, people think that once neural tissue is gone, it doesn't come back,” says Clint Penick, a biologist at Kennesaw State and the study’s lead author, in a statement. “But we found that when workers of the Indian jumping ant switch caste roles, they can both lose and regrow large regions of their brains. Future understanding of the mechanisms involved in these brain changes might shed light on how brain plasticity is controlled in humans, especially with regards to helping regenerate or repair neural damage.”

To study the unique bodily transformation that the Indian jumping ant’s pseudo-queens undergo, the researchers painted a group of 60 pseudo-queens from 30 colonies with different colors to tell them apart. The researchers then separated half of the ants from their colonies and put each one in isolation, reports Troy Farah for National Geographic. The team left the other 30 pseudo-queens—also called called gamergates—with their respective subjects as a control group.

After a few days, the isolated pseudo-queens stopped laying eggs, and after a few weeks the ants began to revert to typical worker behaviors, reports Natalie Grover for the Guardian. At the six- to eight-week mark, Penick and his co-authors dissected the ants that appeared to have given up their temporary royal status and found their ovaries had shrunk back down to normal dimensions and their brains had also grown back to assume their former size.

“There are lots of insects with documented plasticity in all of the traits here—but none that I know of with this level of reversible plasticity,” Emilie Snell-Rood, an evolutionary biologist at the University of Minnesota who wasn’t involved in the research, tells National Geographic. “Many social insects show changes in these brain regions as they transition between phases of their worker life, or move from foraging behavior to queen behavior. But shifting neural investment once, and then back later, is another thing entirely.”

As for why the ants slash their processing power when they assume the throne, Penick tells the Times the pseudo-queen’s royal duties don’t take much in the way of cognitive processing power. Food is brought to them, and defending the nest is someone else’s job.

“Worker ants need a large brain to deal with these cognitive tasks, but gamergates don’t need to think that much,” Penick tells the Times. “Once they win the tournament, they become little more than egg-laying machines.”

As Penick tells the Guardian, the finding that the Indian jumping ant can regrow its brain “opens up opportunities now to dig into the mechanisms that control whether a brain region grows or shrinks in size.”