Data from: Differential gene expression in Acromyrmex leaf-cutting ants after challenges with two fungal pathogens

Social insects in general and leaf-cutting ants in particular have increased selection pressures on their innate immune system due to their social lifestyle and monoclonality of the symbiotic fungal cultivar. As this symbiosis is obligate for both parties, prophylactic behavioural defences against infections are expected to increase either ant survival or fungus-garden survival, but also to possibly trade off when specific infections differ in potential danger. We examined the effectiveness of prophylactic behaviours and modulations of innate immune defences by a combination of inoculation bioassays and genome-wide transcriptomic studies (RNA-Seq), using an ant pathogen (Metarhizium brunneum) and a fungus-garden pathogen (Escovopsis weberi) and administering inoculations both directly and indirectly (via the symbiotic partner). Upon detection of pathogen conidia, ant workers responded by increasing both general activity and the frequency of specific defence behaviours (self-grooming, allo-grooming, garden-grooming) independent of the pathogen encountered. This trend was also evident in the patterns of gene expression change. Both direct and indirect (via fungus garden) inoculations with Metarhizium induced a general up-regulation of gene expression, including a number of well-known immune-related genes. In contrast, direct inoculation of the fungus garden by Escovopsis induced an overall down-regulation of ant gene expression, whereas indirect inoculation (via the ants) did not, suggesting that increased activity of ants to remove this fungus-garden pathogen is costly and involves trade-offs with the activation of other physiological pathways.

总体而言，社会性昆虫尤其是切叶蚁，由于其群居生活方式以及共生栽培真菌的单克隆性，其先天免疫系统（innate immune system）承受了更强的选择压力。鉴于该共生关系对双方均为专性共生，针对感染的预防性行为防御理应提升蚁群或真菌菌圃的存活率，但当不同感染的潜在危害存在差异时，这类防御也可能产生适应性权衡。本研究结合接种生物测定与全基因组转录组学研究（RNA测序，RNA-Seq），探究了预防性行为以及先天免疫防御调控的效果；实验选用了蚁类病原菌布氏绿僵菌（Metarhizium brunneum）与菌圃病原菌埃斯科沃普斯霉（Escovopsis weberi），并分别通过直接接种与间接接种（通过共生伙伴）的方式完成处理。当工蚁检测到病原菌分生孢子后，无论遭遇何种病原菌，均会提升整体活动水平以及特定防御行为（自我梳理、异体梳理、菌圃梳理）的发生频率。这一趋势在基因表达变化模式中同样有所体现。无论是直接还是间接（通过菌圃）接种布氏绿僵菌，均会诱导基因表达整体上调，其中包含多个已知的免疫相关基因。与之形成鲜明对比的是，通过埃斯科沃普斯霉直接接种菌圃会导致蚂蚁基因表达整体下调，而通过蚂蚁间接接种则未出现该现象；这表明蚂蚁为清除该菌圃病原菌而提升活动水平存在代谢成本，且该过程会与其他生理通路的激活产生适应性权衡。