Data from: Interaction specificity between leaf-cutting ants and vertically transmitted Pseudonocardia bacteria

Background: The obligate mutualism between fungus-growing ants and microbial symbionts offers excellent opportunities to study the specificity and stability of multi-species interactions. In addition to cultivating fungus-gardens, these ants have domesticated actinomycete bacteria to defend gardens against the fungal parasite Escovopsis and possibly other pathogens. Panamanian Acromyrmex echinatior leaf-cutting ants primarily associate with actinomycetes of the genus Pseudonocardia. Colonies are inoculated with one of two vertically transmitted strains (Ps1 or Ps2), and maintain the same strain over their lifetime. We performed a cross-fostering experiment to test whether co-adaptations between ants and bacterial strains have evolved, and how this affects bacterial growth and ant prophylactic behavior after infection with Escovopsis. Results: We show that Pseudonocardia readily colonized ants irrespective of their colony of origin, but that the Ps2 strain, which was previously shown to be less invasible by additional bacteria than Ps1, reached a higher final cover when grown on its native host than on alternative hosts. The frequencies of major grooming and weeding behaviors co-varied with symbiont/host combinations, showing that ant behavior also was affected when cuticular actinomycete strains were swapped. Conclusion: These results show that the interactions between leaf-cutting ants and Pseudonocardia bear signatures of mutual co-adaptation within a single ant population.

研究背景：切叶蚁与微生物共生体之间的专性互利共生关系，为探究多物种互作的特异性与稳定性提供了绝佳的研究模型。除培育真菌园之外，这类蚂蚁还驯化了放线菌（actinomycete），用以抵御真菌寄生菌Escovopsis及其他潜在病原菌。巴拿马地区的尖颚切叶蚁（Acromyrmex echinatior）主要与假诺卡氏菌属（Pseudonocardia）的放线菌形成共生关联。其蚁群会通过垂直传播获得Ps1或Ps2两种菌株中的一种，并在整个生命周期中维持该菌株不变。本研究通过交叉抚育实验，旨在验证蚂蚁与细菌菌株间是否演化出协同适应性，并阐明该适应性在感染Escovopsis后对细菌生长及蚂蚁防御行为的影响。
研究结果：本研究发现，无论蚁群来源如何，假诺卡氏菌（Pseudonocardia）均可高效定殖于蚂蚁体表；但相较于Ps1菌株，此前研究表明Ps2菌株更难被其他细菌侵染，且当其在原生宿主上定殖时，最终的体表覆盖面积显著高于在非原生宿主上的覆盖水平。蚂蚁主要的梳毛与除草行为频率会随共生体-宿主组合的差异发生变化，这表明替换体表放线菌菌株后，蚂蚁的行为同样会受到影响。
研究结论：上述结果证实，在单个蚂蚁种群内，切叶蚁与假诺卡氏菌之间的互作存在双向协同适应性的特征。