Veronica Marie Sinotte:
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The social evolution of organisms and the microorganisms they interact with unequivocally shapes the complexity of life. Multicellular organisms evolved from social groups of related cells, and through this major evolutionary transition, interdependent, integrated, complex higher-level individuals such as animals were forged. Similarly, a subsequent transition occurred in cooperative social groups of related insects. The transition resulted in complex colonies known as superorganisms that can also be considered individuals from an evolutionary perspective.
In superorganisms, insects are interdependent, dividing labour between reproductives and helpers, like the organismal germline and soma, and their actions are integrated to promote superorganismal reproduction. These higher-level individuals, organisms and superorganisms, also interact with microbes such as bacteria and fungi, ranging from single species to complex communities of microorganisms. These microbes can be mutualistic, synergistically supporting host metabolism, defence, and development, or parasitic, harming host health and fitness. Consequently, hosts modify interactions with symbiotic microbes to promote beneficial associations, and overall, the interests of both hosts and microbes shape the evolution and ecology of symbioses.
This thesis explores symbioses between superorganismal social insects and their microbial partners. Among superorganismal clades, derived termites, bees, and certain ant species engage in ancient mutualisms with conserved and co-adapted microbes. First, I propose that natural selection at the level of the individual results in analogous mechanisms for microbiome management in superorganisms and multicellular organisms. Next, I examine the impact symbionts have on hosts and the interplay between partners. Lastly, I contributed to two studies that emphasize the ecological importance of these superorganisms and their symbioses. Overall, the thesis clarifies superorganismal symbioses within the framework of major evolutionary transitions, elaborates on interactions between complex hosts and symbiotic communities, and underlines the significance of these symbioses within ecosystems.