A new study suggests that brain and behavior relationships may have changed in a profound way as larger, more complex insect societies evolved from smaller, simpler ones.
Researchers headed by Sean O'Donnell, a University of Washington associate professor of psychology, found that a key region in the brains of a primitively social paper wasp is better developed in dominant females than in subordinate ones.
"This finding, the first of its kind, contrasts with most of the prior work on social insect brain development. Earlier studies, including one of ours, were done on highly social species with large colony sizes. Among these species, age plays an important role in task performance and workers that leave the nest to forage generally have better-developed brains," he said.
"We found the opposite pattern with a primitively social wasp. Here, the stay-at-home dominant females had better brain development. In this species, direct dominance interactions among the females dictate task performance. Dominance and social interactions were more important than foraging tasks in explaining brain development."
In the new study, O'Donnell and colleagues from the University of Texas studied the brain development of the primitively social wasp Mischocyttarus mastigophorus in the tropical cloud forest near Monteverde, Costa Rica. These wasps live in colonies ranging in size from a handful to several dozen individuals where the division of labor is governed by aggression. The researchers examined an area of the insects' brain called the mushroom bodies. There is one mushroom body on top of each hemisphere of the wasp brain and these structures have a vague resemblance to the cerebrum in human and other vertebrates. The researchers were particularly interested in the calyx, a part of the mushroom body where neural connections are made.