Indian Jumping Ants Shrink, Regrow Their Brains to Become Queen of the Colony

Only a few species can shrink their brains, and only a few also can regrow their brains. But Indian jumping ants have both these abilities, a first of its kind ever recorded.

Most ant colonies follow a hierarchy wherein a single queen lays eggs, while the rest manages everything in the colony. Only the queen and male ants can reproduce, while the rest of them are sterile and are tasked to forage for food, nurse baby ants, go to war, and do other tasks for the colony.

The role of ants is already determined even during their larval stage. Whether they become workers or an ant queen, it depends on whether they are fed generously and given the right hormones.

But it is different with Indian jumping ants (Harpegnathos saltator) because ants undergo a reversible process of shrinking their brains for a chance to become the new queen.

"They have this ability to completely transform themselves at the adult stage, and that makes them interesting to try to understand," lead author Dr. Clint Penick from US-based Kennesaw State University said.

The study, entitled "Reversible plasticity in brain size, behavior and physiology characterize caste transitions in a socially flexible ant (Harpegnathos saltator)," is published in the Proceedings of the Royal Society B: Biological Sciences.

The Fight To Be The Next Queen

According to The Guardian, Indian jumping ants commence into a frenzied "ritualized combat" hours after the queen dies to be the colony's next leader.

Ant workers engage in fierce duels that could last for a month that involve jamming their antenna into each other. These chosen workers fighting to be the next queen multitask by fighting fiercely while also activating their ovaries. They are called the pseudo queens or formerly known as gamergates.

Around ten in every 100 ants in a colony are chosen to fight to become queen and see their life expectancy increase from six months to five years. Their ovaries will swell five times their size to fill up their entire abdomen, and their brains shrink by around 20% to 25% of their size, which scientists believe is the way to conserve limited resources to egg production.

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Brain Shrinkage in Animals Might Be More Common Than We Think

Significant brain size changes have also been recorded in few other species like the squirrels during hibernation and some bird, such as the sparrows, according to National Geographic.

White-crowned sparrows can grow 68,000 new neurons when breeding season to help them learn new mating calls. Then the same neurons will also die during winter when food is scarce. By springtime, the cycle repeats.

But this similar mechanism is now only observed in insects. No insect has been observed to have similar brain plasticity and reversible plasticity other than Indian jumping ants.

"Many social insects show changes in these brain regions as they transition between phases of their working life, or move from foraging behavior to queen behavior. But shifting neural investment once, and then back later, is another thing entirely," says Emilie Snell-Rood, an evolutionary biologist at the University of Minnesota.

But scientists believe that these types of reversible brain size changes are not as rare as experts think. Perhaps in the next years, more will be discovered as scientists continue to explore different species on the planet.