_Ever-ready Brainiacs

The study of neural plasticity — a property that all animals’ nervous systems share — provides insights into the dynamics between behavior and the environment.

_Sean O'Donnell

O’Donnell is a professor in the Department of Biodiversity, Earth and Environmental Science in the College of Arts and Sciences.

Tiny termites tower over many other members of the animal kingdom in one respect: the mutability of their brains.

Termite brains have a “mushroom body,” visible in the purple-tinted photomicrograph. It’s a commmand center enabling termites to dig, chew, build, mate and etc. The distinct mushroom body shape can be seen in the photograph (below) of a dampwood termite’s head.

Living inside logs, tree stumps, fence posts or utility poles, most dampwood termites, or Zootermopsis, never see the light of day.

Still, they are some of the most developmentally complex and flexible animals out there, according to Professor Sean O’Donnell, a professor in the Department of Biodiversity, Earth and Environmental Science.

Like other insects, dampwood termites’ brains contain structures called mushroom bodies, which serve as a command center that enables them to dig, chew, build, mate, fly or defend the nest.

The mushroom bodies of individual Zootermopsis differ from one another, based on social roles they fill, and they also change as the insect matures.

Their neural plasticity follows multiple stages of molting before the termites emerge as workers, soldiers or reproductives. Each colony features just one king and one queen. But numerous other members of the colony have a latent capacity to reproduce, too, with the potential to become replacement reproductives, should the king or queen die.

In a 2022 study in Insectes Sociaux, O’Donnell and colleagues Susan J. Bulova and Meghan Barrett measured the brains of different caste members. The researchers found that dampwood termites with the largest mushroom bodies are the worker nymphs — suggesting how cognitively demanding it is to perform tasks for the colony. Other classes of reproductives had smaller mushroom bodies.

O’Donnell’s team also traced unexpected developmental routes.

“Some individuals can molt into being a soldier and then apparently switch to becoming a reproductive,” O’Donnell says. “That’s the last thing you expect to happen. It shows they have even more flexibility than we realized.”

In a separate study published The Science of Nature in 2022, O’Donnell and his colleagues focused on the optic lobes that develop in the brains of kings and queens. The only dampwood termites to leave the nest, the king and queen will fly out to mate and begin a new colony.

A large optic lobe is evident in the brain of a reproductive termite.

This section of a soldier termite brain lacks a prominent optic lobe

The eyes of king and queen dampwood termites are easy to spot on the exterior of the head

This image captures the king or queen’s eyes and brain

Since kings and queens have a unique need to be able to navigate outside the colony, the finding that their brains feature larger optic lobes hardly came as a surprise.

But O’Donnell’s team also found developed optic lobes in the brains of the immature nymphs that will later molt into kings and queens, documenting “experience-expectant brain development” seldom seen among animals.

“With some accuracy, we can predict the developmental future of an individual,” O’Donnell says. “And it looks as though the brain is anticipating the trajectory toward mating flights, although the optic lobe is not being used yet by the nymphs.”

Intriguingly, the researchers also found that the optic lobes stay in place, even after the kings and queens conclude their travels and settle down into their dark nests. The finding is unexpected, O’Donnell explains, since investment in neural tissue is a precious metabolic undertaking that usually comes with a measurable payoff.

“To be quite honest,” he says, “I find it still to be a bit of a head scratcher.”