Use It or Lose It

The following is an article from the Smithsonian Tropical Research Institute’s July 2015 Issue of Tropicos. You can read the full issue here.

STRI Fellow Dr. Sabrina Amador marks ants on an acacia tree

When her colony is young, an acacia ant worker is an expert multitasker. Alongside her nest mates, she defends her home inside an acacia tree seedling, forages for food and tends the brood. But as the tree and the colony grow, she specializes in one of at least three roles: soldier, forager or nurse. Once settled into a single job, she becomes woefully inefficient at doing any of the others.

Her tiny brain undergoes permanent changes making her an expert at one task, according to research by STRI postdoctoral fellow Sabrina Amador. Amador’s work on Pseudomyrmex spinicola ants in the forests around Panama City demonstrates how living in an organized society alters the brain, with implications for other social species, perhaps including humans.

“Experience shapes their brains, which change as they age just as all animal brains do,” says Amador, a two-time STRI fellow who recently completed her Ph.D. at the University of Texas at Austin. “If you’re living as a society, you don’t have to worry about doing all the jobs of a society—you can do just one.”

P. spinicola makes for an especially interesting candidate to study societal brain function because all of the ants are physically the same. Without confounding factors like, for example, the big heads and mandibles that characterize the soldier castes of some other ant species, Amador can directly attribute any differences she finds in the brain to behavior.

Her fieldwork involves countless hours marking ants with paint and observing their behavior to determine their roles in the colony. Amador also tests soldiers — which usually patrol the tree’s lower trunk—in foraging tasks, and foragers—which gather food bodies from the tips of the acacia’s wispy leaves—in defensive tasks, and records their subsequent befuddlement.