Immune challenges increase network centrality in a queenless ant

Social animals display a wide range of behavioural defences against infectious diseases, some of which inherently increase social contacts with infectious individuals (e.g., mutual grooming), while others decrease them (e.g., social exclusion). These defences often rely on the detection of infectious individuals, but this can be achieved in several ways that are difficult to differentiate. Here, we combine non-pathogenic immune challenges with automated tracking in colonies of the clonal raider ant to ask whether ants can detect the immune status of their social partners and to quantify their behavioural responses to this perceived infection risk. We first show that a key behavioural response elicited by live pathogens (allogrooming) can be qualitatively recapitulated by immune challenges alone. Automated scoring of interactions between all colony members reveals that this behavioural response increases the network centrality of immune-challenged individuals through a general increase in physical contacts. These results show that ants can detect the immune status of their nestmates and respond with a general “caring” strategy, rather than avoidance, towards social partners that are perceived to be infectious. Finally, we find no evidence that changes in cuticular hydrocarbon profiles drive these behavioural effects.

Methods
Survival of individuals was scored manually. Grooming received by focal ants was manually scored from video recordings using BORIS software 5.1.0. Other behavioural metrics were calculated from automatedly tracked trajectories of all ants recorded with the tracking software anTraX. Mass spectra of cuticular hydrocarbons were acquired and analysed with the software ChemStation G1701AA v. A.03.00.

社会性动物演化出多样化的行为防御策略以对抗传染病：其中部分策略会天然增加与感染个体的社交互动（如相互理毛），另一部分则会减少此类接触（如社会排斥）。此类防御行为通常依赖于对感染个体的识别，但其识别路径多样且难以区分。本研究将非致病性免疫刺激与克隆劫掠蚁（clonal raider ant）群体的自动化追踪技术相结合，旨在探究蚂蚁能否识别社交伙伴的免疫状态，并量化其对感知到的感染风险的行为响应。本研究首先证实，活体病原体诱发的核心行为响应——异体理毛（allogrooming），仅通过免疫刺激即可在定性层面重现。通过对蚁群全体个体间的互动开展自动化评分，研究发现该行为响应通过全面提升物理接触频率，提升了接受免疫刺激个体的社交网络中心性。上述结果表明，蚂蚁能够识别巢伴的免疫状态，并对被感知为具有感染性的社交伙伴采取普适性的“关怀”策略，而非回避行为。最后，本研究未发现表皮碳氢化合物（cuticular hydrocarbon）谱的变化是此类行为效应的介导因素。
方法
个体存活情况通过人工评分记录。目标蚂蚁所获得的理毛行为，通过BORIS 5.1.0软件对录像进行人工评分。其余行为指标则通过追踪软件anTraX记录的所有蚂蚁的自动化追踪轨迹计算得到。表皮碳氢化合物的质谱数据通过ChemStation G1701AA v. A.03.00软件采集并分析。