Social Complexity and Brain Evolution: Comparative Analysis of Modularity and Integration in Ant Brain Organization

Abstract

The behavioral demands of living in social groups have been linked to the evolution of brain size and structure, but how social organization shapes investment and connectivity within and among functionally specialized brain regions remains unclear. To understand the influence of sociality on brain evolution in ants, a premier clade of eusocial insects, we statistically analyzed patterns of brain region size covariation as a proxy for brain region connectivity. We investigated brain structure covariance in young and old workers of two formicine ants, the Australasian weaver ant Oecophylla smaragdina, a pinnacle of social complexity in insects, and its socially basic sister clade Formica subsericea. As previously identified in other ant species, we predicted that our analysis would recognize in both species an olfaction-related brain module underpinning social information processing in the brain, and a second neuroanatomical cluster involved in nonolfactory sensorimotor processes, thus reflecting conservation of compartmental connectivity. Furthermore, we hypothesized that covariance patterns would reflect divergence in social organization and life histories either within this species pair or compared to other ant species. Contrary to our predictions, our covariance analyses revealed a weakly defined visual, rather than olfactory, sensory processing cluster in both species. This pattern may be linked to the reliance on vision for worker behavioral performance outside of the nest and the correlated expansion of the optic lobes to meet navigational demands in both species. Additionally, we found that colony size and social organization, key measures of social complexity, were only weakly correlated with brain modularity in these formicine ants. Worker age also contributed to variance in brain organization, though in different ways in each species. These findings suggest that brain organization may be shaped by the divergent life histories of the two study species. We compare our findings with patterns of brain organization of other eusocial insects.

Cerebrotypes in Cephalopods: Brain Diversity and Its Correlation With Species Habits, Life History, and Physiological Adaptations

“…Third, behavior and ecology could be instrumental in determining cephalopod "cerebrotypes" such that species occupying similar niches exhibit similar brain composition. Similarity reflecting niche type has been found in vertebrates (e.g., Gonzalez-Voyer et al, 2009b;Schuppli et al, 2016;Hamodeh et al, 2017;Kamhi et al, 2019) and it is reasonable to assume that it could also occur in Cephalopoda, the invertebrates with the highest degree of brain centralization.…”

Active Inferants: An Active Inference Framework for Ant Colony Behavior

“…Only foragers were included in this model, future derivations could include worker developmental trajectories and colony-level task allocation processes (Friedman et al, 2020a ; Hayakawa et al, 2020 ). Nestmate-level behavioral heuristics are important for colony efficiency (Gordon et al, 2019 ; Kamhi et al, 2019 ; Arganda et al, 2020 ), as are truly colony-level processes (e.g., dynamic interaction patterns and nest architectures (Gordon, 2010 ; Pinter-Wollman et al, 2018 ; Lemanski et al, 2019 ) are in tight feedback with nestmate-level development and task allocation. Our model could be extended to study the role of these processes in the evolution of colony behavior, since the proposed simulation involved only agent-environment stigmergic interaction.…”

Putting the ecology back into insect cognition research

“…Despite many attempts to correlate brain sizes with metrics of social complexity in different insect taxa, empirical supports for a social brain hypothesis are mixed (Farris, 2016;Gordon et al, 2019;Kamhi et al, 2019Kamhi et al, , 2016O'Donnell et al, 2015;Riveros et al, 2012).…”