Data from: Excavation and aggregation as organizing factors in de novo construction by mound-building termites

Termites construct complex mounds that are orders of magnitude larger than any individual and fulfil a variety of functional roles. Yet the processes through which these mounds are built, and by which the insects organize their efforts, remain poorly understood. The traditional understanding focuses on stigmergy, a form of indirect communication in which actions that change the environment provide cues that influence future work. Termite construction has long been thought to be organized via a putative ‘cement pheromone’: a chemical added to deposited soil that stimulates further deposition in the same area, thus creating a positive feedback loop whereby coherent structures are built up. To investigate the detailed mechanisms and behaviours through which termites self-organize the early stages of mound construction, we tracked the motion and behaviour of major workers from two Macrotermes species in experimental arenas. Rather than a construction process focused on accumulation of depositions, as models based on cement pheromone would suggest, our results indicated that the primary organizing mechanisms were based on excavation. Digging activity was focused on a small number of excavation sites, which in turn provided templates for soil deposition. This behaviour was mediated by a mechanism of aggregation, with termites being more likely to join in the work at an excavation site as the number of termites presently working at that site increased. Statistical analyses showed that this aggregation mechanism was a response to active digging, distinct from and unrelated to putative chemical cues that stimulate deposition. Agent-based simulations quantitatively supported the interpretation that the early stage of de novo construction is primarily organized by excavation and aggregation activity rather than by stigmergic deposition.

白蚁能够构筑远超出单个白蚁个体数个数量级的复杂蚁冢，并承担多种功能性作用。然而，此类蚁冢的构筑过程，以及昆虫协调群体劳作的具体机制，目前仍知之甚少。传统认知聚焦于迹径通讯（stigmergy）——一种间接通讯形式，即通过改变环境的行为提供提示信号，以影响后续劳作行为。长期以来，学界认为白蚁的筑巢行为由一种假定的‘水泥信息素’调控：这类化学物质会被添加到已沉积的土壤中，刺激该区域进一步沉积土壤，由此形成正反馈循环，最终构筑出结构规整的整体结构。为探究白蚁自组织开展蚁冢构筑早期阶段的具体机制与行为模式，我们在实验场域（experimental arenas）中追踪了两个大白蚁属（Macrotermes）物种的大型工蚁的运动与行为。与基于水泥信息素的模型所预言的、以沉积物积累为核心的筑巢过程截然不同，我们的研究结果显示，群体组织的核心机制实则以挖掘活动为基础。挖掘行为集中于少量挖掘位点，这些位点随后成为土壤沉积的模板。该行为由聚集机制介导：当某一挖掘位点当前正在劳作的白蚁数量增多时，后续白蚁更倾向于加入该位点的劳作。统计分析表明，这种聚集机制是对活跃挖掘行为的响应，与此前假定的可刺激沉积的化学信号截然不同且毫无关联。基于智能体的模拟（agent-based simulations）从定量层面佐证了这一解读：从头构建（de novo construction）蚁冢的早期阶段，主要由挖掘与聚集活动主导，而非依赖迹径通讯介导的沉积行为。