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.