Dimensions: Identifying how the ecological and evolutionary interactions between host and symbiont shape holobiont biodiversity

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Although individual animals have long been considered a fundamental unit of evolution, we now know that each is really a co-dependent collection of host animal and microbes. This co-dependency reaches from ancient times through to the present day. Many animals depend on gut bacteria to process food and incorporate essential nutrients into the host's own tissues. To untangle the importance of this partnership for hosts and symbiotic gut bacteria, this project will study a diverse and ecologically important social animal group, the turtle ants. As social organisms, ants and humans share ways for acquiring helpful and harmful bacteria. State-of-the-art molecular and genomic methods will be used to investigate ancient and modern influences on the symbiosis, the function of the bacteria for host health, and the means of passage and maintenance of the bacterial symbionts over millions of years.Explaining global patterns of biodiversity and their drivers have long been central challenges in the fields of ecology and evolution. Increasingly, it is becoming apparent that biodiversity is itself a function of interactions across different levels of biological organization. Among the metazoans, symbioses with microbes are a defining feature, and individuals are integrated collections of host and symbiont cells, together defining the "holobiont". By studying the diverse and tractable turtle ant system, this research will address the relationships between symbiosis and the dimensions of holobiont biodiversity with unprecedented clarity. Specifically, this research will address: 1) the roles of time, biogeography, and habitat in host diversification (host taxonomic dimension); 2) variation in gut communities across host ant phylogeny, geography, habitat, and ecological niches (symbiont taxonomic dimension integrated with host taxonomic and functional dimensions); 3) the extent of codiversification for ~10 core, host-specific symbiont lineages, and the impacts of host phylogeny, geography, and ecology on symbiont transfer (symbiont taxonomic dimension integrated with host taxonomic and functional dimensions); 4) variation in genome evolution and innovation across symbionts with varying degrees of codiversification, and across genes with varying function (taxonomic, genetic, and functional integration of hosts and symbionts); and 5) symbiont function in light of symbiont genome evolution, host-symbiont codiversification, and host phylogeny, geography, and ecology (taxonomic, genetic, and functional integration of hosts and symbionts).