The impact of host metapopulation structure on short-term evolutionary rescue in the face of a novel pathogenic threat

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While most evolutionary studies of host-pathogen dynamics consider pathogen evolution alone or host-pathogen coevolution, there is evidence that hosts can evolve more rapidly than their pathogen during initial outbreaks after disease introduction, e.g. evolutionary rescue in the short term. In these cases, spatial, temporal and epidemiological factors could all affect the evolutionary dynamics of the host population. To help inform potential conservation policies in the near-term, we considered the case of one pathogen introduced into a metapopulation of hosts with two genotypes: wild type and robust in which there is a tradeoff in disease-driven mortality and spatial mobility. We employed a classic Susceptible-Infected model and explored how differences in mortality and migration affect the representation of host genotypes and total host population persistence. We find that greater difference in disease-driven mortality between the two host types increases the probability of evolutionary rescue, but there is a point after which disease-driven mortality is so high as to drive the disease prevalence below the reproductive threshold, ending the outbreak and therefore benefitting the wild type. Migration reduces the chance of evolutionary rescue by reducing the competition between the two host genotypes when the difference in disease-driven mortality is sufficiently small, but at larger differences migration acts primarily as a facilitator of disease spread, increasing the probability of evolutionary rescue, though significantly decreasing the total size of the surviving population. This study reveals that both epidemiology and metapopulation ecology can play critical roles in host evolution during the emergence of a novel infection and provide guidance for host conservation and disease control.