Department of Biology, Centre for Social Evolution, University of Copenhagen, Copenhagen, Denmark.
Mol Ecol. 2013 Apr;22(8):2173-87. doi: 10.1111/mec.12255. Epub 2013 Mar 8.
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.
一般来说，社会性昆虫，特别是切叶蚁，由于其社会生活方式和共生真菌品种的单克隆性，对其先天免疫系统施加了更大的选择压力。由于这种共生关系对双方都是强制性的，因此可以预期预防性的行为防御措施会增加蚂蚁的生存或真菌花园的生存，但当特定的感染在潜在危险方面存在差异时，也可能会产生权衡。我们通过接种生物测定和全基因组转录组学研究（RNA-Seq）的组合，使用一种蚂蚁病原体（Metarhizium brunneum）和一种真菌花园病原体（Escovopsis weberi），并直接和间接（通过共生伙伴）进行接种，检查了预防性行为和先天免疫防御的调节效果。在检测到病原体孢子时，蚂蚁工蚁通过增加一般活动和特定防御行为（自我梳理、异体梳理、花园梳理）的频率来做出反应，而与遇到的病原体无关。这种趋势在基因表达变化模式中也很明显。直接和间接（通过真菌花园）接种 Metarhizium 都会诱导基因表达的普遍上调，包括许多众所周知的免疫相关基因。相比之下，直接接种真菌花园的 Escovopsis 会导致蚂蚁基因表达的全面下调，而间接接种（通过蚂蚁）则不会，这表明蚂蚁为了清除这种真菌花园病原体而增加的活动是有代价的，并且涉及到与其他生理途径的激活的权衡。
