Ant Brood Function as Life Preservers during Floods

Social organisms can surmount many ecological challenges by working collectively. An impressive example of such collective behavior occurs when ants physically link together into floating ‘rafts’ to escape from flooded habitat. However, raft formation may represent a social dilemma, with some positions posing greater individual risks than others. Here, we investigate the position and function of different colony members, and the costs and benefits of this functional geometry in rafts of the floodplain-dwelling ant Formica selysi. By causing groups of ants to raft in the laboratory, we observe that workers are distributed throughout the raft, queens are always in the center, and 100% of brood items are placed on the base. Through a series of experiments, we show that workers and brood are extremely resistant to submersion. Both workers and brood exhibit high survival rates after they have rafted, suggesting that occupying the base of the raft is not as costly as expected. The placement of all brood on the base of one cohesive raft confers several benefits: it preserves colony integrity, takes advantage of brood buoyancy, and increases the proportion of workers that immediately recover after rafting.社会性生物可通过集体协作克服诸多生态挑战。此类集体行为的典型范例之一，便是蚂蚁通过躯体相互联结形成漂浮“筏体”，以此逃离被洪水淹没的栖息环境。然而，筏体的形成可能构成一种社会困境：部分个体所处的位置会使其承担远高于其他同类的风险。本研究针对栖息于洪泛平原的塞氏林蚁（Formica selysi）展开探究，旨在明确该蚁种筏体中不同巢群成员的位置与功能，以及这种功能构型的成本与收益。我们通过在实验室中诱导蚁群形成筏体，观察到如下现象：工蚁均匀分布于筏体各处，蚁后始终处于筏体中心，且所有蚁群幼体（brood）均被置于筏体底部。通过一系列实验，我们证实工蚁与蚁群幼体具备极强的抗浸没能力；且筏体形成后，二者均保有极高的存活率，这表明占据筏体底部的个体所需承担的代价并不如预期那般高昂。将所有幼体集中放置于单一紧密结合的筏体底部，可带来多重益处：一是维持巢群的结构完整性，二是利用幼体的漂浮特性，三是提升筏体形成后能够快速恢复活力的工蚁占比。