The role of continuous geography in parasite local adaptation
Authors: Bob Week; Gideon Bradburd
Affiliation: Michigan State University, East Lansing Michigan
Keywords: Coevolution
Previous work modelling the consequences of interactions between gene-flow, random genetic drift and coevolution on local adaptation in host-parasite systems have made use of metapopulation models where geography is discretized and dispersal is global. These studies generally conclude that increased rate of gene-flow for the parasite relative to the host yields parasite local adaptation. The colloquial explanation for this result is that increased dispersal can lead to increased genetic variance and thus promote adaptive capacity. However, this explanation ignores the effect of continuous versus discrete geography and how patterns of limited versus global dispersal interact with drift to determine which species is locally adapted. To close this gap we present a phenotypic model of host-parasite coevolution in continuous space with finite local population densities. We find the parasite is locally adapted to its host when its average dispersal distance is shorter than the average dispersal distance of the host. Performing a similar analysis on a metapopulation model of host-parasite trait coevolution where dispersal is global and genetic variance is held constant, we recover the classical result described above. This highlights the role of geography and in particular suggests a subtle distinction between the effects of dispersal rate and dispersal distance on parasite local adaptation.