An Exploration of the Social Brain Hypothesis in Insects

Lihoreau, Mathieu; Latty, Tanya; Chittka, Lars

doi:10.3389/fphys.2012.00442

Cited by 103 publications

(94 citation statements)

References 72 publications

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“…The MBs are crucial for testing the SBH, as they are involved in multisensory integration, memory and learning, which would be of larger size for processing the increased social stimuli in larger colonies in all society members, regardless of task specialization [19,38,39]. In contrast to this prediction of the SBH, but consistent with the TSH, we found a taskdependent effect of colony size and specialization on the relative size of regions within the MB's calyces (figure 4).…”

Section: (A) Behavioural Tests Of Task Specialization Hypothesismentioning

confidence: 99%

Specialization and group size: brain and behavioural correlates of colony size in ants lacking morphological castes

et al. 2015

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Group size in both multicellular organisms and animal societies can correlate with the degree of division of labour. For ants, the task specialization hypothesis (TSH) proposes that increased behavioural specialization enabled by larger group size corresponds to anatomical specialization of worker brains. Alternatively, the social brain hypothesis proposes that increased levels of social stimuli in larger colonies lead to enlarged brain regions in all workers, regardless of their task specialization. We tested these hypotheses in acacia ants (Pseudomyrmex spinicola), which exhibit behavioural but not morphological task specialization. In wild colonies, we marked, followed and tested ant workers involved in foraging tasks on the leaves (leaf-ants) and in defensive tasks on the host tree trunk (trunk-ants). Task specialization increased with colony size, especially in defensive tasks. The relationship between colony size and brain region volume was task-dependent, supporting the TSH. Specifically, as colony size increased, the relative size of regions within the mushroom bodies of the brain decreased in trunk-ants but increased in leaf-ants; those regions play important roles in learning and memory. Our findings suggest that workers specialized in defence may have reduced learning abilities relative to leaf-ants; these inferences remain to be tested. In societies with monomorphic workers, brain polymorphism enhanced by group size could be a mechanism by which division of labour is achieved.

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Section: (A) Behavioural Tests Of Task Specialization Hypothesismentioning

confidence: 99%

Specialization and group size: brain and behavioural correlates of colony size in ants lacking morphological castes

et al. 2015

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“…Nevertheless, cuticular hydrocarbons function in nestmate [59][60][61] and social role [62] discrimination; these recognition mechanisms may be more highly developed in socially complex species because advanced division of labour can generate morphologically or behaviourally variable worker groups and thus require greater discriminatory capabilities to support colony-level functions. The neural mechanisms underlying these social processes and others remain unclear [63], and it is therefore difficult to determine their precise role in brain evolution.…”

Section: Discussion (A) Social Brain Theory and Ant Brain Evolutionmentioning

confidence: 99%

Social complexity influences brain investment and neural operation costs in ants

et al. 2016

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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.

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“…Moreover, abstract cognitive abilities previously thought to be exclusive to the repertoires of large-brained vertebrates or some cephalopods [14] have recently been demonstrated in insects [15]. Neural network models suggest that increases in cognitive complexity that intuitively seem to require extensive neural expansion and thus large brains, such as those that accompany the evolution of sociality, may actually require few neurons and only subtle changes in the local neural circuitry underlying specific ancestral behaviours (reviewed in [16]). Therefore, size-related constraints on nervous system performance may be less stringent than previously assumed, allowing very small animals to evolve relatively complex behaviour.…”

Section: Introductionmentioning

confidence: 99%

Investment in higher order central processing regions is not constrained by brain size in social insects

et al. 2014

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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.

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An Exploration of the Social Brain Hypothesis in Insects

Cited by 103 publications

References 72 publications

Specialization and group size: brain and behavioural correlates of colony size in ants lacking morphological castes

Specialization and group size: brain and behavioural correlates of colony size in ants lacking morphological castes

Social complexity influences brain investment and neural operation costs in ants

Investment in higher order central processing regions is not constrained by brain size in social insects

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