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，由于其社会性生活方式以及共生栽培真菌的单克隆性，其先天免疫系统承受了更强的选择压力。由于这种共生关系对双方均为专性依赖，因此针对感染的预防性行为防御，理应提升蚂蚁自身或菌圃的存活率；但当不同感染的潜在危险性存在差异时，这类防御可能会产生权衡取舍。本研究通过接种生物测定与全基因组转录组学研究（RNA-Seq）相结合的方法，选用蚂蚁病原菌（Metarhizium brunneum）与菌圃病原菌（Escovopsis weberi），并分别通过直接与间接（通过共生伙伴）两种方式实施接种，以此探究预防性行为与先天免疫防御调控的有效性。当检测到病原菌分生孢子时，工蚁会提升整体活动水平，并增加特异性防御行为（自我理毛、互理毛与菌圃理毛）的发生频率，且该反应不受所接触病原菌种类的影响。这一趋势同样体现在基因表达的变化模式中。无论是直接接种还是通过菌圃间接接种布鲁姆金龟子绿僵菌（Metarhizium brunneum），均会引发基因表达的整体上调，其中包含多个已知的免疫相关基因。与之形成对比的是，通过韦伯埃斯科沃菌（Escovopsis weberi）直接接种菌圃，会导致蚂蚁的基因表达整体下调；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的活动存在代谢成本，并会与其他生理通路的激活产生权衡取舍。