"Symbiosis is the close and long-term interaction between different biological species. Insects are among the best model systems for studying symbioses as their immune systems appear to be relatively tolerant to invasion and their niches are often so specialized that microbial symbionts can satisfy important metabolic needs. Laboratories across the world often specialize either in the molecular biology of host-symbiont interactions in specific insect models, or in the evolutionary biology of parasitic or mutualistic symbioses taking a broader approach. This proposal is meant to build bridges between these domains, by applying advanced molecular methods to resolve fundamental evolutionary questions of symbiosis in a social insect model system. My research will focus on an almost completely unknown component of the symbiosis between attine ants and their fungus-gardens: the bacterial communities in the guts of these ants that likely fulfill complementary roles in the symbiosis. Objectives are to identify these bacteria, to localize them when they are tissue-specific, and to compare their functional roles across several attine genera that represent different stages of advancement of the symbiosis. I will use qPCR, FISH and TEM to identify putative symbionts, metatranscriptomic techniques to characterize the cumulative bacterial genes that are expressed in the ant guts, and qRT-PCR and RNAi to clarify some of the functional roles of ant and microbial genes that are expressed in the guts. The research that I propose is highly multi-disciplinary, as it combines a wide range of state-of-the-art molecular techniques with conceptual hypotheses from social evolution theory. This combination is feasible because my training in molecular microbiology of fruit-fly and aphid symbionts is combined with the renowned expertise of my host in the evolutionary biology of attine fungus-growing ants. The work proposed will be facilitated by annotated genomes of these ants being available."