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.

中文翻译：

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社会复杂性和大脑进化：蚂蚁脑组织模块化和整合性的比较分析。

生活在社会群体中的行为要求已经与大脑大小和结构的演变联系在一起，但是尚不清楚社会组织如何影响功能专门的大脑区域内部和内部的投资和连通性。为了了解社交性对蚂蚁（一种共生昆虫的主要进化枝）的大脑进化的影响，我们对大脑区域大小协变的模式进行了统计分析，以作为大脑区域连通性的代理。我们调查了两种蚁蚁的年轻和老工人的大脑结构协方差，这两种是澳大利亚昆虫的社会复杂性的巅峰，其是澳大利亚的织叶蚁蚁Oecophylla smaragdina及其社会基本姐妹进化枝甲。正如先前在其他蚂蚁物种中发现的那样，我们预测，我们的分析将在两种物种中都识别出与嗅觉相关的大脑模块，这些模块支撑着大脑中的社会信息处理，并且还识别出第二个参与非嗅觉感觉运动过程的神经解剖簇，从而反映了隔室连通性的保守性。此外，我们假设协方差模式将反映该物种对内或与其他蚂蚁物种相比在社会组织和生活史上的差异。与我们的预测相反，我们的协方差分析揭示了两个物种中视觉，而不是嗅觉感觉处理集群的定义都较弱。这种模式可能与对巢外工人行为表现对视觉的依赖以及与视球的相关扩展以满足两种物种的航行需求有关。另外，我们发现，在这些蚁蚁中，菌落的大小和社会组织是衡量社会复杂性的关键指标，与脑模块性的关系很小。工人的年龄也促进了大脑组织的变化，尽管每种物种以不同的方式。这些发现表明，两种研究物种的不同生活史可能会影响大脑的组织。我们将我们的发现与其他正常社会昆虫的大脑组织模式进行比较。