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，在于可提升对捕食者的警戒能力。过往研究已针对群体规模效应（group size effect）展开探究：即随着群体规模扩大，个体警戒水平会下降，但群体整体探测捕食者的能力并未受损。然而，目前针对个体站位是否能提升群体集体警戒能力的相关研究仍相对匮乏。

我们以真社会性蜜蜂（eusocial bee）狭翅无刺蜂（Tetragonisca angustula）为研究对象，探究了其警戒行为的协调性及其对捕食者探测的影响。该物种的蜂巢由两类守卫蜂负责防御：一类是在蜂巢入口上方盘旋的守卫蜂，它们会在入侵者抵达入口前完成探测并拦截；另一类则直接驻守于入口处。

研究发现，盘旋守卫蜂的站位并非随机分布，而是呈现出强烈的两侧数量均等的分布倾向。这种站位布局可提升守卫蜂群体的集体警戒能力：当入口两侧的守卫蜂数量比例均衡时，群体的整体视野范围要优于两侧数量比例失衡的守卫群体。

最后，我们通过生物测定实验（bioassay）证实：当守卫蜂分布在入口两侧时，其在入侵者抵达入口前完成探测的能力会得到提升。

综上，我们的研究结果为“警戒行为具有协调性”这一结论提供了强有力的证据，且这种协调性可优化蜂巢防御效果。相较于其他集群生活的动物，其个体警戒行为往往带有自利性，且会面临觅食等存在时间冲突的约束条件；而真社会性昆虫工蜂的利他属性，极有可能推动了协调式警戒行为的演化——正如本研究中狭翅无刺蜂所展现的这一现象。