Coevolution · The genomic signature of rapid coevolution within a wild host-parasite system

Parasites infect nearly all forms of metazoan life, and act to shape the evolution of host populations and drive the dynamics of entire biological communities. Parasitism also acts a 2-way street: As host populations evolve in response to selection imposed by their parasites, so too does the parasite evolve in response to its host. This antagonistic coevolution between host and parasite may generate much of the genetic diversity found in natural populations, and is likely a strong driver of local adaptation and population differentiation. Host-parasite coevolution is also of enormous practical concern for human society, as parasites impose considerable costs in respect to agriculture, livestock production, aquaculture, and human health. Unfortunately though, very little empirical evidence is available to evaluate some of the most fundamental predictions of coevolutionary theory, especially in respect to the genomic basis of coevolution, as past studies of antagonistic coevolution have typically been conducted at the phenotypic level, or using simplified host-parasite systems in a laboratory setting. I therefore propose to conduct a direct genome-level investigation of antagonistic coevolution between wild populations of a host (Daphnia magna) and its bacterial parasite (Pasteuria ramosa). This research will capitalize upon recent technical and theoretical advances in the D. magna / P. ramosa system, and will center upon the measurement of interspecies linkage disequilibrium across the genomes of both species. This investigation will be conducted across multiple timescales: A single point in time, across the course of one year, and across a 50-year sediment core time-series. I expect that these experiments will yield direct genomic evidence of antagonistic coevolution in a natural population, a clear test of Red Queen coevolutionary dynamics, and the first genetic time-series of such resolution and duration.