Social brains may have evolved very differently in insects than in vertebrates.
The society you live in can shape the complexity of your brain–and it does so differently for social insects than for humans and other vertebrate animals.
A new comparative study of social and solitary wasp species suggests that as social behavior evolved, the brain regions for central cognitive processing in social insect species shrank. This is the opposite of the pattern of brain increases with sociality that has been documented 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 published today in Proceedings of the Royal Society B.
Essentially, O’Donnell says the cooperative or integrative aspects of insect colonies, such as information sharing among colony mates, can reduce the need for individual cognition in these societies.
The distributed cognition hypothesis contrasts sharply with leading models of how vertebrate animals’ social complexity relates to their cognitive abilities. In vertebrates, more complex social environments generally demand more complex cognitive abilities in individuals. Social brain theorists have described the idea behind this increasing complexity as “Machiavellian intelligence.” The idea in such social challenge hypotheses is that competition between individuals drives the evolution of sharper intelligence, as vertebrate societies tend to involve associations between unrelated individuals who experience both conflict over resources and opportunities to form alliances. Individuals who navigate such challenges with stronger cognitive abilities have a survival advantage.
O’Donnell’s team recognized that societies can 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.
They looked at whether social insects’ more cooperative social structures might have different effects on brain evolution. They compared brains of 29 related wasp species from Costa Rica, Ecuador and Taiwan, including both solitary species and social species with varied colony structures and sizes. It is the first study informed by evolutionary relationships between species to comparatively test social brain models in social insects.
The society you live in can shape the complexity of your brain. For vertebrate animals like humans, and even birds and fish, there is a lot of support for the idea that our complex brains developed along with complex societies.
Compared to social species, they found solitary species had significantly larger brain parts known as the mushroom bodies, which are used for multisensory integration, associative learning and spatial memory–the best available measure of complex cognition in these insects. The finding supports the idea that, as insect social behavior evolved, the need for such complex cognition in individuals actually decreased.
“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.
Funding: The research was funded by the National Science Foundation.
Source: Rachel Ewing – Drexel University
Image Credit: Image credited to Sean O’Donnell
Video Source: The video is available at the Drexel University YouTube page
Original Research: Abstract for “Distributed cognition and social brains: reductions in mushroom body investment accompanied the origins of sociality in wasps (Hymenoptera: Vespidae)” by Sean O’Donnell, Susan J. Bulova, Sara DeLeon, Paulina Khodak, Skye Miller, and Elisabeth Sulger in Proceedings of the Royal Society B. Published online June 17 2015 doi:10.1098/rspb.2015.0791
Distributed cognition and social brains: reductions in mushroom body investment accompanied the origins of sociality in wasps (Hymenoptera: Vespidae)
The social brain hypothesis assumes the evolution of social behaviour changes animals’ ecological environments, and predicts evolutionary shifts in social structure will be associated with changes in brain investment. Most social brain models to date assume social behaviour imposes additional cognitive challenges to animals, favouring the evolution of increased brain investment. Here, we present a modification of social brain models, which we term the distributed cognition hypothesis. Distributed cognition models assume group members can rely on social communication instead of individual cognition; these models predict reduced brain investment in social species. To test this hypothesis, we compared brain investment among 29 species of wasps (Vespidae family), including solitary species and social species with a wide range of social attributes (i.e. differences in colony size, mode of colony founding and degree of queen/worker caste differentiation). We compared species means of relative size of mushroom body (MB) calyces and the antennal to optic lobe ratio, as measures of brain investment in central processing and peripheral sensory processing, respectively. In support of distributed cognition predictions, and in contrast to patterns seen among vertebrates, MB investment decreased from solitary to social species. Among social species, differences in colony founding, colony size and caste differentiation were not associated with brain investment differences. Peripheral lobe investment did not covary with social structure. These patterns suggest the strongest changes in brain investment—a reduction in central processing brain regions—accompanied the evolutionary origins of eusociality in Vespidae.
“Distributed cognition and social brains: reductions in mushroom body investment accompanied the origins of sociality in wasps (Hymenoptera: Vespidae)” by Sean O’Donnell, Susan J. Bulova, Sara DeLeon, Paulina Khodak, Skye Miller, and Elisabeth Sulger in Proceedings of the Royal Society B. Published online June 17 2015 doi:10.1098/rspb.2015.0791