Supplementary Material for: Linking Colony Size with Foraging Behavior and Brain Investment in Odorous Ants (Formicidae: Dolichoderinae)

Superorganisms represent a unique level of biological organization in which the phenotype of the reproductive unit, the colony, results from traits expressed at the level of individual workers. Because body size scaling has important consequences for cell diversity and system complexity in solitary organisms, colony size is a trait of particular interest in superorganism evolution. In some instances, division of labor and worker polymorphism scale with colony size, but in general little is known about how colony size drives differences in individual-level behavior or neural traits. Ants represent the greatest diversity of superorganisms and provide a manner of natural experiment to test trends in trait evolution across multiple instances of colony size expansion. In this study, we control for environmental differences and worker size polymorphism to test if colony size correlates with measures of foraging behavior and brain size in dolichoderine ants. We present data from 3 species ranked by colony size. Our results suggest colony size correlates with measures of exploratory behavior and brain investment, with small-colony ants showing higher exploratory drive and faster exploration rate than the larger colony species, and greater relative investment in the primary olfactory brain region, the antennal lobe, than the larger colony species.

超有机体（superorganisms）代表了一种独特的生物组织层级：其繁殖单元——群落——的表型，源自个体工蚁所表达的性状。由于体型缩放规律对独居生物的细胞多样性与系统复杂性具有重要影响，因此群落规模是超有机体演化研究中备受关注的核心性状。在部分案例中，劳动分工与工蚁多型性会随群落规模发生缩放，但总体而言，学界对群落规模如何调控个体行为或神经性状的差异仍知之甚少。蚂蚁类群拥有最为多样的超有机体形式，为我们在多个群落规模扩张的自然实例中检验性状演化规律提供了理想的天然实验体系。本研究通过控制环境差异与工蚁体型多型性，检验臭蚁亚科（Dolichoderinae）蚂蚁的群落规模是否与其觅食行为指标及脑容量存在关联。本研究共纳入3种按群落规模排序的蚂蚁物种并提供对应实验数据。研究结果表明，群落规模与蚂蚁的探索行为指标及脑投资存在显著关联：相较于大群落物种，小群落蚂蚁展现出更强的探索驱动力与更快的探索速度，且在主要嗅觉脑区——触角叶（antennal lobe）——中的相对脑投资更高。