Data from: Social complexity influences brain investment and neural operation costs in ants

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.

支撑适应性行为所需的神经组织的产生与运作的代谢消耗，被视作大脑演化过程中的重要选择压力。在灵长类动物中，大脑尺寸与群体规模呈正相关，这一现象大概率源于大型社会中复杂社会关系对认知能力的更高要求。
真社会性昆虫（eusocial insects）的社会复杂性同样与大型群体、集体智能以及不育工蚁的劳动分工密切相关。然而，超有机体表型（superorganism phenotypes）或可降低行为特化的工蚁的认知负荷，进而推动选择出大脑尺寸更小、或大脑代谢能量成本更低的个体。
为验证该假说，我们对比了两种社会组织模式迥异的蚂蚁物种的大脑投资模式，以及作为ATP使用量替代指标的细胞色素氧化酶（cytochrome oxidase, COX）活性。社会结构复杂的黄猄蚁（Oecophylla smaragdina）工蚁，相较于社会结构更基础的丝光褐林蚁（Formica subsericea）工蚁，不仅大脑尺寸更大，且在作为高阶感觉处理区的蕈形体（mushroom bodies, MBs）中的相对投资更高。但黄猄蚁工蚁的蕈形体中COX活性有所降低。
我们的研究结果表明，与灵长类动物类似，蚂蚁的群体规模同样与更大的大脑尺寸存在关联。然而，社会结构复杂的黄猄蚁在代谢成本高昂的脑组织上的投资成本有所升高，但这一成本似乎通过能量消耗的降低得到了抵消。