Insect Brains Shrink in Groups: Speedy but Less Complex

Wasps are not greater philosophers when they're in social groups, researchers say. That is, these insects think less deeply when they're involved in work groups or otherwise efficient, according to a new study by Drexel University researchers.

As social behavior evolved among wasps, the brain regions for central cognitive processing in social insect species shrank, the study found. This is, by the way, the opposite of the pattern of brain increases with sociality that has been recorded for several kinds of vertebrate animals, including mammals, birds and fish.

"By relying on group mates, insect colony members may afford to make less individual brain investment. We call this the distributed cognition hypothesis," said Sean O'Donnell, PhD, a professor in the Drexel University College of Arts and Sciences who led the study, as reported in Science Daily.

Essentially, efficiency by way of information sharing among colony mates and other cooperative aspects of insect colonies, can reduce the need for individual thought.

Among vertebrates, more complex social environments tend to demand more complex cognitive abilities.

Insect colonies, form in different ways. "Unlike most vertebrate societies, insect colonies are usually family groups--offspring that stay and help their parents. Although there can be family strife, the colony often succeeds or fails as a unit," O'Donnell said, in Science Daily.

The study compared brains of 29 related wasp species from Costa Rica, Ecuador and Taiwan, looking at both solitary species and social species with varied colony structures and sizes.

In the case of insects, solitary species had much larger brain parts known as the mushroom bodies. These are used for multisensory integration, associative learning and spatial memory-and they are the best available measure of complex cognition in these insects.

"The challenge now is to test whether the pattern of reduced mushroom body investment holds up in other lineages of social insects. Termites and roaches, and solitary versus social bees, are good places to look," said O'Donnell, in Science Daily.