Patterns of Specificity of the Pathogen Escovopsis across the Fungus-Growing Ant Symbiosis

Parasites evolve within complex abiotic and biotic environments. Because of this, it is often challenging to ascertain how evolutionary and ecological processes together affect parasite specialization. Here, we use the fungus-growing ant system, which consists of ancient, likely coevolved, complex communities, to explore the ecological and evolutionary forces shaping host-parasite specificity. We use a comparative phylogenetic framework to determine whether patterns of specificity between the fungal parasite Escovopsis and its host fungi at fine phylogenetic scales reflect patterns of specificity at broader phylogenetic levels. In other words, we ask whether parasite specificity across broad host phylogenetic relationships is maintained by specificity toward more closely related hosts. We couple this exploration with manipulations of the community context within which host-parasite interactions are taking place to evaluate how community complexity alters parasite specificity. Regardless of host community complexity, parasites displayed a consistent pattern of specialization on native hosts, that is, those that they are found attacking in nature, with the potential for occasional switching to hosts distantly related to their native hosts. These results suggest that, even within a complex community context, pairwise host and parasite adaptation and coadaptation can be the primary drivers of the evolution and maintenance of parasite specificity.