Labile associations between fungus-growing ant cultivars and their garden pathogens

Abstract

The distribution of genetic and phenotypic variation in both hosts and parasites over their geographic ranges shapes coevolutionary dynamics. Specifically, concordant host and parasite distributions facilitate localized adaptation and further specialization of parasite genotypes on particular host genotypes. We here compare genetic population structure of the cultivated fungi of the fungus-growing ant Apterostigma dentigerum and of the cultivar-attacking fungus, Escovopsis, to determine whether these microbial associations have evolved or are likely to evolve genotypegenotype specialization. Analyses based on amplified fragment length polymorphism (AFLP) genotyping of host cultivars and pathogenic Escovopsis from 77 A. dentigerum colonies reveal that populations of hosts and pathogens are not similarly diverged and that host and pathogen genetic distances are uncorrelated, indicating that genetically similar parasites are not infecting genetically similar hosts. Microbial bioassays between pathogens and cultivars of different genotypes and from different populations show little pairwise specificity; most Escovopsis strains tested can successfully infect all cultivar strains with which they are paired. These molecular and experimental data suggest that Escovopsis genotypes are not tightly tracking cultivar genotypes within the A. dentigerum system. The diffuse nature of this host-pathogen association, in which pathogen genotypes are not interacting with a single host genotype but instead with many different hosts, will influence evolutionary and ecological disease dynamics of the fungus-growing ant-microbe symbiosis.

Specialized Fungal Parasites and Opportunistic Fungi in Gardens of Attine Ants

“…strain can be associated with many genera of ants and vice versa, demonstrating that the interrelationship is apparently nonspecific or weak at a finer phylogenetic level [50,51]. Even in the same nest, different Escovopsis strains can be found as confirmed in the work of Taerum et al [52], who verified that 67% of the colonies of Atta sp.…”

Microbial secondary metabolites and their impacts on insect symbioses

“…However, it does not explicitly incorporate eco-evolutionary processes such as dispersal limitation through vertical transmission and host selection that have both been demonstrated for this symbiosis [32,33 ,57]. Interestingly, the fungus-growing ant symbiotic network contains taxa likely occupying different positions on the eco-evolutionary spectrum due to different modes of transmission, for example, Escovopsis (horizontal) versus Pseudonocardia and the cultivar (vertical) [32,61]. Incorporating both ecological and evolutionary dynamics in models of symbiotic community assembly and tying them specifically to the molecular pathways mediating community interactions remains important challenges for future research.…”

Growth and Conidiation Response of Escovopsis weberi (Ascomycota: Hypocreales) Against the Fungal Cultivar of <I>Acromyrmex lundii</I> (Hymenoptera: Formicidae)

“…We measured the growth and conidiation levels of E. weberi in the presence and absence of Leucoagaricus. Our prediction was that E. weberi would be an efÞcient pathogen against all the cultivar isolates tested based on results obtained previously by others (Gerardo et al 2004, Gerardo and Caldera 2007, Taerum et al 2007. We also expected that E. weberi, as an efÞcient pathogen, would be able to respond accordingly by maximizing its growth and conidiation when detecting the presence of its host, Leucoagaricus sp.…”