Data from: Soldiers in a stingless bee: work rate and task repertoire suggest they are an elite force

The differentiation of workers into different morphological sub-castes (e.g. soldiers) represents an important evolutionary transition and is thought to improve division of labor in social insects. Soldiers occur in many ant and termite species where they make up a small proportion of the workforce. A common assumption of worker caste evolution is that soldiers are behavioral specialists. Here, we report the first test of the “rare specialist” hypothesis in a eusocial bee. Colonies of the stingless bee Tetragonisca angustula are defended by a small group of morphologically differentiated soldiers. Contrary to the “rare-specialist” hypothesis, we found that soldiers worked more (+34-41%) and performed a greater variety of tasks (+23-34%) than other workers, particularly early in life. Our results suggest a “rare elite” function of soldiers in T. angustula, i.e. they perform a disproportionately large amount of the work. Division of labor was based on a combination of temporal and physical castes, but soldiers transitioned faster from one task to the next. We discuss why the “rare specialist” assumption might not hold in species with a moderate degree of worker differentiation.

工蜂分化为不同形态学亚品级（如兵虫）是社会性昆虫演化历程中的重要过渡事件，被认为可优化其劳动分工体系。兵虫广泛分布于多种蚂蚁和白蚁类群中，种群占比通常较低。关于工蜂品级演化的主流假设认为，兵虫属于行为特化类群。本研究首次针对真社会性蜂类（eusocial bee）开展"稀有特化者"假说（rare specialist hypothesis）的实证检验。无刺蜂Tetragonisca angustula的蜂群由一小群形态特化的兵虫负责守卫。与"稀有特化者"假说相悖，我们发现兵虫的劳作时长较普通工蜂高出34%至41%，且承担的任务种类也多出23%至34%，这一现象在其成虫早期尤为显著。本研究结果表明，Tetragonisca angustula中的兵虫实则承担着"稀有精英"的职能：它们所完成的劳动量远超其种群占比。该蜂群的劳动分工基于时序品级与形态品级的协同作用，但兵虫的任务转换速度显著快于普通工蜂。本文还探讨了为何"稀有特化者"这一普遍假设，在工蜂分化程度中等的类群中并不成立。