Parasites (defined broadly to include viruses, bacteria, protozoans and others) infect nearly all forms of life and act as a powerful force to shape the evolution of host populations and drive the dynamics of biological communities. As host populations evolve in response to their parasites, so too does the parasite evolve in response to its host. This antagonistic coevolution between host and parasite may be responsible for much of the genetic diversity found in natural populations, and is likely a strong driver of local adaptation and population differentiation. Coevolution between host and parasite is also of enormous practical concern for human society, as parasites impose considerable costs in respect to agriculture, livestock production, aquaculture, and human health. In this research, we aim to extend beyond the scope of previous coevolutionary studies and 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 capitalizes upon recent technical and theoretical advances in the D. magna / P. ramosa model system, and centers upon the measurement of interspecies linkage disequilibrium (here called: interlinkage) across the genomes of both species. Interlinkage is a novel term, which we have defined as a statistical association of alleles across the genomes of separate coevolving species. Although interlinkage has not been formally defined previously, it arises from basic theoretical expectations when coevolutionary dynamics are governed by matching allele interactions (e.g. the likely mode of infection for D. magna / P. ramosa).
Despite arising as a fundamental aspect of some coevolutionary models, interlinkage remains an entirely theoretical construct as it has never been studied within natural populations. This research aims to identify and characterize the signal of interlinkage between wild populations of host (D. magna) and parasite (P. ramosa), and to evaluate this signal across multiple timescales. We 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. The study of interlinkage will furthermore provide opportunity for the identification of new genomic regions important for some host-parasite interactions.
