title: Investment in higher order central processing regions is not constrained by brain size in social insects.
abstract: The extent to which size constrains the evolution of brain organization and the genesis of complex behaviour is a central, unanswered question in evolutionary neuroscience. Advanced cognition has long been linked to the expansion of specific brain compartments, such as the neocortex in vertebrates and the mushroom bodies in insects. Scaling constraints that limit the size of these brain regions in small animals may therefore be particularly significant to behavioural evolution. Recent findings from studies of paper wasps suggest miniaturization constrains the size of central sensory processing brain centres (mushroom body calyces) in favour of peripheral, sensory input centres (antennal and optic lobes). We tested the generality of this hypothesis in diverse eusocial hymenopteran species (ants, bees and wasps) exhibiting striking variation in body size and thus brain size. Combining multiple neuroanatomical datasets from these three taxa, we found no universal size constraint on brain organization within or among species. In fact, small-bodied ants with miniscule brains had mushroom body calyces proportionally as large as or larger than those of wasps and bees with brains orders of magnitude larger. Our comparative analyses suggest that brain organization in ants is shaped more by natural selection imposed by visual demands than intrinsic design limitations.
authors.affiliation: Undergraduate Program in Neuroscience, Boston University, , 2 Cummington Mall, Boston, MA 02215, USA, Department of Neuroscience, University of Arizona, , 611 Gould-Simpson Science Building, Tucson, AZ 85721, USA, Department of Science and Education, Field Museum of Natural History, , 1400 South Lake Shore Drive, Chicago, IL 60605, USA, Department of Biology, Boston University, , 5 Cummington Mall, Boston, MA 02215, USA.
authors.forename: Mario L
authors.initials: ML
authors.lastname: Muscedere
authors.forename: Wulfila
authors.initials: W
authors.lastname: Gronenberg
authors.forename: Corrie S
authors.initials: CS
authors.lastname: Moreau
authors.forename: James F A
authors.initials: JF
authors.lastname: Traniello
mesh_terms: D000818:Animals; D001000:Ants / Q000033:anatomy & histology / Q000502:physiology*; D001516:Bees / Q000033:anatomy & histology / Q000502:physiology*; D005075:Biological Evolution; D049628:Body Size; D001921:Brain / Q000033:anatomy & histology / Q000502:physiology; D003071:Cognition; D009929:Organ Size; D014863:Wasps / Q000033:anatomy & histology / Q000502:physiology*
keywords: allometry; ants; mushroom bodies
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