The Indian jumping ant Harpegnathos Saltator has many talents. Found in floodplains across India, this centimeter-long arthropod has a vertical leap of four inches and the ability to kill prey almost twice its size. If that wasn’t enough, these amazing ants can resize their own brains too.
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 nearly 20 percent and shrink in just a few weeks. Although other insects, including honeybees, are known to 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 ant species use this ability to prepare their bodies for reproduction.
Like most ant colonies, the Indian jumping ants are made up of a queen, males for breeding, and an all-female working class. The queen has the most desirable position in the colony. Not only are queens hand and foot serviced by worker ants, but they also live more than five times longer. And in a typical colony, the queen is the only woman allowed to have offspring.
For most species of ants, queens are born, not made. Indian jumping ants, however, are one species that allows worker ants to fight for a chance to become a king.
When an Indian jumping ant dies, about 70 percent of the women in their colony participate in a battle royale tournament that lasts up to 40 days, in which participants beat each other with their antennae until a group of five to ten winners emerges . These winners can spend the rest of their days doing nothing but pumping babies.
Once the tournament begins, hormones drive participants into an intense physiological transformation that turns them into reproductive ants known as gamergates. Although worker ants and gamergates are similar in size, their internal anatomy is vastly different.
“If you look inside their bodies, you can see the tremendous changes they are going through,” said Clint Penick, assistant professor of biology at Kennesaw State University in Georgia and lead author of the new study.
Dr. Penick and colleagues compared the internal anatomy of workers and gamergates and found that becoming a gamergate not only caused worker ants’ ovaries to grow five times their normal size, but also caused their brains to shrink by about 20 percent .
The researchers then used laser-assisted imaging technology to examine gamergates’ brains and found that their optical lobes exhibited the greatest amount of shrinkage during their transformations. 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 is no need for them to maintain the ability to process visual signals,” said Dr. Penick.
Workers turning into gamergates also noticed significant shrinkage of their central brains. Dr. Penick believes this is because the gamergates don’t have to perform cognitively difficult tasks like finding food and defending the nest from predators.
“Worker ants need big brains to handle these cognitive tasks, but gamergates don’t have to think too much,” he said. “Once they win the tournament, they become little more than egg-laying machines.”
The researchers believe that 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. His noodle grows back in the spring.
“Operating the brain is an expensive organ,” 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 the evolution of the brain in other species of ants, believes that when female Indian jumping ants are transformed into gamergates, most of the energy once spent on the brain is diverted to parts of the body responsible for reproduction.
To determine whether this redistribution of resources was reversible, Dr. Penick and his colleagues found several newly transformed gamergates and isolated them from their colonies.
“I thought they would probably just die, but within a few days they switched back completely,” said Dr. Penick. “It was pretty amazing to see that they were able to fully expand their brains to exactly the size they were before.”
The researchers suggest that the ability to switch between worker and gamergate likely evolved to ensure that those who fail to fulfill their offerings to the queen can return to their previous role in maintaining the colony.
“This species shows an incredible amount of plasticity, both in the larval and adult stages,” said Dr. Penick. “And because of this, they can be a model for understanding things like epigenetics and the control of plasticity in organisms, even down to humans.”
