| Microbial symbionts play key roles in shaping the diversity of life, from disease causing pathogens to beneficial microbes. The fungus-growing ant (Attini, Apterostigma dentigerum) is ideal for exploring these dynamics, as it maintains multiple symbionts, including fungal cultivars, cultivar attacking pathogens, and mutualistic bacteria whose antibiotic secretions combat infection. Decades of Attine-symbiont research has characterized these interactions as examples of diffuse coevolution. By contrast, coevolutionary theory on a geographic scale posits that these diffuse associations may still contain tightly coevolved interactions in a mosaic pattern over space. Moreover, these mosaics are shaped by the population genetic structure of interacting species. In this dissertation, I characterize the Apterostigma dentigerum -symbiont dynamic from a geographic mosaic prospective. The history of attine-symbiont evolutionary ecology is reviewed in chapter 1. In chapter 2, I describe cultivar-pathogen population structure and suggest that this labile association may facilitate specific adaptation by the mutualistic bacteria, Pseudonocardia. In chapter 3, I describe the population genetic structure of Pseudonocardia and demonstrate that its fine scale phylogeograpic structure may facilitate local adaptation with a common pathogen ( Escovopsis) morphotype. Chapter 4 uses bioassay inhibition experiments in combination with population genomic approaches to demonstrate that the Pseudonocardia-Escovopsis interaction is consistent with a geographic mosaic of coevolution, with a locally adapted population residing on Barro Colorado Island in Panama. Chapter 5 provides a putative framework and future directions for understanding the role biosynthetic gene clusters play in Pseudonocardia-pathogen coevolution. These studies provide insights into the maintenance of antibiotic potency over evolutionary time, and microbial niche evolution. |
