Data from: Distributed cognition and social brains: reductions in mushroom body investment accompanied the origins of sociality in wasps (Hymenoptera: Vespidae)

The social brain hypothesis assumes the evolution of social behavior changes animals’ ecological environments, and predicts evolutionary shifts in social structure will be associated with changes in brain investment. Most social brain models to date assume social behavior imposes additional cognitive challenges to animals, favoring the evolution of increased brain investment. Here we present a modification of social brain models which we term the distributed cognition hypothesis. Distributed cognition models assume group members can rely on social communication instead of individual cognition; these models predict reduced brain investment in social species. To test this hypothesis we compared brain investment among 29 species of wasps (Vespidae family) including solitary species and social species with a wide range of social attributes (i.e., differences in colony size, mode of colony founding, and degree of queen/worker caste differentiation). We compared species means of relative size of mushroom body calyces (MB), and the antennal to optic lobe ratio, as measures of brain investment in central processing and peripheral sensory processing, respectively. In support of distributed cognition predictions, and in contrast to patterns seen among vertebrates, mushroom body investment decreased from solitary to social species. Among social species, differences in colony founding, colony size, and caste differentiation were not associated with brain investment differences. Peripheral lobe investment did not covary with social structure. These patterns suggest the strongest changes in brain investment- a reduction in central processing brain regions- accompanied the evolutionary origins of eusociality in Vespidae.

社会脑假说（social brain hypothesis）认为，社会行为的演化会改变动物的生态环境，并预测社会结构的演化转变将与脑投资的变化相关联。迄今为止，多数社会脑模型均假定社会行为会给动物带来额外的认知挑战，从而推动脑投资提升的演化进程。本文我们提出一种对社会脑模型的改良版本，并将其命名为分布式认知假说（distributed cognition hypothesis）。分布式认知模型假定群体成员可借助社会沟通替代个体认知，这类模型预测社会性物种的脑投资会有所降低。为验证该假说，我们对29种胡蜂（胡蜂科Vespidae）的脑投资水平进行了比较，样本涵盖独居物种与社会性物种，且后者具备多样的社会属性（即群体规模、筑群模式以及蜂王/工蜂品级分化程度的差异）。我们分别以蘑菇体萼（mushroom body calyces，MB）的相对体积，以及触角叶与视神经叶的比值，作为中枢加工与外周感觉加工相关脑投资的衡量指标，并比较了各物种的对应均值。与脊椎动物中的相关模式相悖，研究结果支持分布式认知假说的预测：从独居物种到社会性物种，蘑菇体的脑投资呈下降趋势。在社会性物种内部，筑群模式、群体规模以及品级分化的差异并未与脑投资差异存在关联。外周感觉脑区的脑投资并未随社会结构发生共变。上述模式表明，胡蜂科真社会性（eusociality）演化起源过程中，伴随的脑投资变化最为显著——即中枢加工相关脑区的体积缩减。