In perhaps the most astounding change of all, the ants’ brain shrinks by about 20 to 25 percent in volume when they become gamergates. (For humans, that’d be the rough equivalent of losing a hunk of brain the size of two tennis balls.) The downsizing isn’t uniform: The insects appear to selectively jettison bits of their brain devoted to hunting, foraging, spatial mapping, and the anty equivalent of critical thinking—a move that likely reroutes precious bodily resources to the ovaries. Jumping-ant brains are already quite small, about a tenth of a cubic millimeter in volume. But brain tissue is “very energetically costly,” Floria Mora-Kepfer Uy, an entomologist at the University of Rochester, told me. And when the future of the colony is at stake, every calorie counts. “There’s a trade-off between reproduction and cognition,” Uy said. It is a heavy crown to wear atop a newly lightened head.
Given the triple threat of casual incest, sororal dueling, and what amounts to a self-inflicted prenatal lobotomy, the whole affair might sound a touch unpalatable to us humans. But in some ways, being a gamergate is downright cushy. These ants are the colony’s VIPs, and their social status is abundantly clear. When gamergates stroll among their subjects, they walk slowly and deliberately, standing high on their legs; workers scuttle out of their way to make room. “They have a royal attitude” about them, Jürgen Liebig, an animal behaviorist at Arizona State University and Penick’s former adviser, told me. “Once you know what to look for, it’s very conspicuous.”
And for any gamergate that’s not vibing her new digs, there is, under certain circumstances, an out. In a new paper published today in Proceedings of the Royal Society B, Penick, Liebig, and their colleagues report that the gamergate transformation is entirely reversible, down to the mind-boggling changes the ants’ brain tissue undergoes. When the researchers isolated gamergates from their colonies, depriving them of the social signals needed to maintain their über-fertile status, then reintroduced them to their peers, the ants rapidly regressed into workers. Their ovaries shriveled, leaving room for their venom glands to grow; their brains ballooned out. They reacquired their aggressive fighting acumen, and would once again jump when provoked. Functionally sterilized and juiced back up with intellect, they became once again indistinguishable from their commoner kin.
The wild flexibility of the ants’ brain is “especially cool,” Lindsey Lopes, a biologist at Rockefeller University who studies ant behavior, and wasn’t involved in the new research, told me. Scientists have found a small handful of other animals that can toggle through brain sizes. Songbirds will bloat their brain ahead of breeding season to help them learn sexy tunes for their mates, only to pare away the excess tissue once the deed is done; hamsters and shrews will cull brain tissue to help conserve energy during hibernation, then restore the lost matter when they awaken in the spring. But reversible changes are unprecedented among insects, which were previously known to add or subtract, but not both, in a single individual. In the insect realm, “I’ve never heard of something [like] a brain shrinking, and then reverting back to a bigger size,” Lopes told me. “That’s a lot of change.”