Kamhi J Frances, Gronenberg Wulfila, Robson Simon K A, Traniello James F A
Department of Biology, Boston University, Boston, MA 02215, USA
Graduate Program for Neuroscience, Boston University, Boston, MA 02215, USA.
Proc Biol Sci. 2016 Oct 26;283(1841). doi: 10.1098/rspb.2016.1949.
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.
产生和运作适应性行为所需神经组织的代谢消耗被认为是大脑进化中的一股重要选择力量。在灵长类动物中，大脑大小与群体规模呈正相关，这大概是由于大型社会中复杂社会关系对认知的更高要求。群居昆虫的社会复杂性也与大群体以及不育工蚁之间的集体智慧和劳动分工有关。然而，超个体表型可能会降低对行为专业化工蚁的认知要求，从而导致对减小大脑大小和/或降低大脑代谢能量成本的选择。为了验证这一假设，我们比较了两种社会组织不同的蚂蚁物种的大脑投资模式和细胞色素氧化酶（COX）活性（ATP使用情况的一个指标）。社会结构复杂的黄猄蚁工蚁比社会结构更简单的丝光蚁工蚁大脑更大，且对蘑菇体（MBs）——高级感觉处理区域——的相对投资更多。然而，黄猄蚁工蚁的蘑菇体中COX活性较低。我们的结果表明，与灵长类动物一样，蚂蚁的群体规模与大脑大小相关。然而，在社会结构复杂的黄猄蚁中，对代谢成本高昂的脑组织投资增加的成本，似乎被能量成本的降低所抵消。
