Individual trial data on path choice in response to risk in Linepithema humile

Ant colonies are likely able to access food locations by multiple paths that can vary predictably in length or mortality risk. To favor one path over another requires ants to perceive, communicate and act upon important differences in length and risk between paths.  Here we present replicate Linepithema humile colonies with four equal-length paths to a sugar source.  The paths vary in probabilities of encountering a risk cue that range from 0 to 100%.  The risk cues were either live workers of an aggressive competitor (Liometopum occidentale: LO) or only formic acid (FA), a defensive chemical common in many formicine species.  Both the probabilities of encounter and type of cue affected path preferences.  Although across both cues the zero-risk path was most used, the use was not exclusive and patterns of response to the cues differed significantly.  More ants were on all the paths when the cue was LO rather than FA, leading to a higher success rate at finding food.  Worker numbers on paths with LO did decline over time as consistent with recognizing neighbors to be ‘dear enemies’ that are a reduced threat to the colony. Similarly, changes in path usage suggested that the FA cue also became viewed as less threatening over time when competitors were never simultaneously present. The results are consistent with L. humile exhibiting the behavioral plasticity and communicative ability needed to categorize and predict risk in order to efficiently collect food while defending against other ant species.

蚁群通常可通过多条路径抵达食物源，各路径的长度或死亡风险可呈现可预测的差异。若要优先选择某一路径而非其他，蚂蚁需要感知、传递信息，并依据路径间长度与风险的显著差异做出相应行动。本研究设置了重复实验的阿根廷蚁（Linepithema humile）蚁群群体，该群体拥有四条长度均等的路径通往糖源。各路径遭遇风险信号的概率介于0至100%之间。此类风险信号分为两类：一类为攻击性竞争者西方林蚁（Liometopum occidentale: LO）的活体工蚁，另一类则仅为甲酸（FA）——一种在众多蚁亚科物种中广泛分布的防御性化学物质。路径偏好同时受到遭遇概率与信号类型的影响。尽管两类信号组中，零风险路径均为使用频率最高的路径，但蚂蚁的选择并非排他性的，且对两类信号的响应模式存在显著差异。当风险信号为LO时，所有路径上的工蚁数量均多于FA信号组，该组的觅食成功率也更高。携带LO信号的路径上的工蚁数量随时间推移逐渐减少，这与蚂蚁将同类识别为‘亲爱敌人’（即对蚁群威胁更低的个体）的行为模式相符。类似地，路径使用模式的变化表明，当竞争者从未同时出现时，FA信号也会随时间推移被视为威胁更低的对象。本研究结果表明，阿根廷蚁具备行为可塑性与信息交流能力，能够对风险进行分类与预测，从而在高效采集食物的同时抵御其他蚁类的侵扰。