title: Social complexity influences brain investment and neural operation costs in ants.
abstract: The metabolic expense of producing and operating neural tissue required for adaptive behaviour is considered a significant selective force in brain evolution. In primates, brain size correlates positively with group size, presumably owing to the greater cognitive demands of complex social relationships in large societies. Social complexity in eusocial insects is also associated with large groups, as well as collective intelligence and division of labour among sterile workers. However, superorganism phenotypes may lower cognitive demands on behaviourally specialized workers resulting in selection for decreased brain size and/or energetic costs of brain metabolism. To test this hypothesis, we compared brain investment patterns and cytochrome oxidase (COX) activity, a proxy for ATP usage, in two ant species contrasting in social organization. Socially complex Oecophylla smaragdina workers had larger brain size and relative investment in the mushroom bodies (MBs)-higher order sensory processing compartments-than the more socially basic Formica subsericea workers. Oecophylla smaragdina workers, however, had reduced COX activity in the MBs. Our results suggest that as in primates, ant group size is associated with large brain size. The elevated costs of investment in metabolically expensive brain tissue in the socially complex O. smaragdina, however, appear to be offset by decreased energetic costs.
authors: Department of Biology, Boston University, Boston, MA 02215, USA franne.kamhi@mq.edu.edu.|Graduate Program for Neuroscience, Boston University, Boston, MA 02215, USA.
authors: J Frances
authors: 0000-0002-3806-0506
authors: JF
authors: Kamhi
authors: Department of Neuroscience, University of Arizona, Tucson, AZ 85721, USA.
authors: Wulfila
authors: W
authors: Gronenberg
authors: Zoology and Ecology, James Cook University, Townsville, Queensland 4811, Australia.
authors: Simon K A
authors: 0000-0001-8870-1933
authors: SK
authors: Robson
authors: Department of Biology, Boston University, Boston, MA 02215, USA.|Graduate Program for Neuroscience, Boston University, Boston, MA 02215, USA.
authors: James F A
authors: JF
authors: Traniello
mesh_terms: D000818:Animals; D001000:Ants / Q000502:physiology*; D001921:Brain / Q000502:physiology*; D003071:Cognition; D003576:Electron Transport Complex IV / Q000502:physiology; D004734:Energy Metabolism; D024521:Mushroom Bodies / Q000502:physiology; D009929:Organ Size; D012919:Social Behavior
chemical_list: D003576:Electron Transport Complex IV
keywords: collective intelligence; cytochrome oxidase; metabolic cost; polymorphism; social brain evolution