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These ants shrink their brains for a chance to become queen

The Indian jumping ant Harpegnathos saltator has many talents. This one-inch-long arthropod, found in flood plains across India, has a four-inch vertical leap and the ability to kill prey nearly twice its size. If that wasn’t enough, these amazing ants can also adjust the size of their own brains.

In a study, published Wednesday in the journal Proceedings of the Royal Society B, scientists found that Indian jumping ants can shrink their brains by as much as 20% and shrink them within weeks. Although other insects, including honey bees, have the ability to increase their brain size, the Indian jumping ant is the first insect known to be able to both increase and decrease brain size. . The researchers behind the study say that females of the ant species use this ability to prepare their bodies for reproduction.

Like most ant colonies, Indian jumping ant colonies consist of a queen, breeding males, and an all-female working class. The queen occupies the most coveted position in the colony. Not only are the queens expected on site by worker ants, but they also live more than five times longer. And in a typical colony, the queen is the only female allowed to have offspring.

For most species of ants, queens are born and not made. However, Indian jumping ants are a species that allows worker ants to compete for a chance to become royal.

When an Indian jumping ant queen dies, around 70% of the women in her colony take part in a battle royale style tournament that lasts up to 40 days where contestants fight with their antennae until a group of five to 10 winners emerge. These overcomers spend the rest of their days doing nothing but pumping babies.

From the start of the tournament, hormones push competitors to undergo an intense physiological transformation that transforms them into queen-type reproductive ants, called gamergates. Although worker ants and gamergates are similar in size, their internal anatomy is very different.

“If you look inside their bodies, you can see the huge transformations they are going through,” said Clint Penick, assistant professor of biology at Kennesaw State University in Georgia and lead author of the short story. study.

Dr Penick and his colleagues compared the internal anatomy of workers and gamergates and found that becoming gamergate not only swelled the ovaries of worker ants up to five times their normal size, but also their brains. shrunk by about 20%.

The researchers then used laser-assisted imaging technology to study the brains of gamergates and found that, during their transformations, their optic lobes suffered the greatest shrinkage. Dr Penick attributes this to the fact that gamergates don’t need good eyesight in their underground nests.

“They live in total darkness, so there’s no reason for them to maintain the ability to process visual signals,” Dr. Penick said.

Workers who transformed into gamergates also experienced significant central brain shrinkage. Dr Penick believes this is because gamergates don’t have to perform cognitively difficult tasks, such as finding food and defending the nest from predators.

“Worker ants need large brains to cope with these cognitive tasks, but gamergates don’t need to think so much,” he says. “Once they win the tournament, they become little more than laying machines.”

Researchers believe these ants shrink their brains to conserve energy, a behavior also seen in Etruscan shrews, a tiny mammal that loses brain size in winter to keep other parts of its body warm. He then regrows his noodles in the spring.

“The brain is an expensive organ to operate,” said James Traniello, a professor of biology at Boston University who was not involved in the study. “It takes a lot of energy.”

Dr Traniello, who studies brain evolution in other ant species, believes that when Indian jumping ants turn into gamergates, most of the energy that was once spent in the brain is diverted to parts of the brain. bodies responsible for reproduction.

To see if this reallocation of resources was reversible, Dr Penick and his colleagues collected several newly transformed gamergates and isolated them from their colonies.

“I thought they were probably going to die, but within days they came back completely,” Dr Penick said. “It was quite amazing to see that they were able to completely re-enlarge their brains to exactly the same size they were before.”

Researchers suspect that the ability to switch between worker and gamergate has likely evolved to ensure that those who fail in their bidding to be queen can return to their previous role of maintaining the colony.

“This species shows an incredible amount of plasticity, both in the larval stage and in the adult stage,” said Dr Penick. “And for this reason, they can be a model for understanding things like epigenetics and plasticity control in organisms, even on a human scale.”

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