Data from: Organisation enhances collective vigilance in the hovering guards of Tetragonisca angustula bees

One benefit of group living is vigilance against predators. Previous studies have investigated the group size effect, where individual vigilance decreases as group size increases without reducing the overall ability of the group to detect predators. However, there has been comparatively little research on whether the positioning of individuals can improve the collective vigilance of the group. We studied the coordination of vigilance and its effect on predator detection in the eusocial bee Tetragonisca angustula. Nests are defended by hovering guards that detect and intercept intruders before they reach the nest entrance, in addition to those that stand upon it. We show that hovering guards are positioned non-randomly, with a strong tendency for equal numbers on both sides of the entrance. This organisation increases the collective vigilance of the guard group, as groups distributed in an even ratio, either side of the entrance, have a greater collective field of view than groups that deviate from an even ratio. Last, we use a bioassay to show that when guards are on both sides of the entrance, their ability to detect intruders before they reach the entrance increases. Overall, our results provide strong evidence that vigilance is coordinated, and that this improves nest defence. Whereas other group-living animals are often selfish in their individual vigilance behaviours, and face competing time constraints such as foraging, the altruistic nature of eusocial insect workers has likely facilitated the evolution of coordinated vigilance, as documented here in T. angustula.

集群生活的优势之一在于提升对捕食者的群体警戒能力。既往研究已针对群体大小效应展开了充分探讨：即随着群体规模扩大，个体的警戒水平会随之降低，但群体整体侦测捕食者的能力并未受到削弱。然而，针对个体空间位置是否能够优化群体集体警戒能力的相关研究仍相对匮乏。本研究以真社会性蜜蜂（eusocial bee）Tetragonisca angustula为实验对象，探究其警戒行为的协调性及其对捕食者侦测的影响。该物种的蜂巢由悬停守卫蜂（hovering guards）与驻守守卫蜂共同防御：悬停守卫蜂会在入侵者抵达蜂巢入口前完成侦测与拦截，驻守守卫蜂则直接驻守于入口处。研究发现，悬停守卫蜂的空间分布并非随机，而是显著倾向于在入口两侧保持近乎均等的种群数量。这种分布模式能够提升守卫蜂群体的集体警戒能力，因为入口两侧守卫蜂数量分布均等的群体，相较于数量偏离均等比例的群体，拥有更广的集体视野范围。最后，本研究通过生物测定实验（bioassay）证实，当守卫蜂均匀分布于入口两侧时，其在入侵者抵达入口前完成侦测的能力会得到显著提升。综上，本研究结果提供了强有力的证据，证明该物种的警戒行为具有协调性，且这种协调性能够有效优化蜂巢防御效果。与其他集群生活的动物不同，后者往往在个体警戒行为中表现出自私性，且需应对觅食等相互冲突的时间约束；而真社会性昆虫工蜂所具备的利他天性，可能推动了协调性警戒行为的演化，正如本研究在T. angustula中所证实的那样。