Darwin's image of the entangled bank captures foremost the pervasiveness of life as it clothes the earth, but it also captures how intimately species interact and often depend on one another. This interaction is particularly pronounced for obligate parasites, who's livelihoods depend on interactions with their hosts and who's hosts often pay severely. In my thesis, I first demonstrate how antagonistic coevolution in Avida leads to a diverse set of interacting host and parasite phenotypes: a digital entangled bank. Second, I show how further evolution is embedded within this community context by studying the coevolution of complexity driven by parasites'population genetic memory -- where the diversifying community of parasites "remembers" previously evolved hosts. Continuing to study the intersection of coevolution and community ecology, I investigate the structure of communities produced by the coevolutionary process in Avida. I show that a nested structure of interactions is common in our experiments, which is the same structure often found in natural host-parasite and plant-pollinator communities as well as many phage-bacteria interaction networks. In addition, I show that "growing" networks are nested by virtue of the process of incrementally adding nodes and edges. Thus, coevolution is expected to produce significantly nested communities when compared to random networks. However, the coevolved digital host-parasite networks are significantly more nested than expected from this neutral growth process. The interactions between hosts and their intimately interacting partners are not just parasitic, instead they span a broad range and include many mutualistic interactions. In the last section of my thesis, I study evolution and coevolution along the parasitism-mutualism continuum using a temperate λ phage system that provides its host with access to an otherwise unavailable metabolic pathway. Instead of evolving more mutualistic phage as I predicted, both the phage and bacteria evolved cheating strategies.
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