Variation in resistance and virulence among demes of a plant host–pathogen metapopulation

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Abstract
Summary: Despite the recognition that spatial structure can have major consequences for the ecological and evolutionary dynamics of host–pathogen interactions, few empirical studies have examined how regional processes affect within‐population co‐evolutionary patterns. Considerable variation was detected within and among demes of a metapopulation in the resistance ofLinum marginaleto a range of local isolates of the rustMelampsora lini.Only four resistance phenotypes were common (occurring at an overall frequency of > 5%) and pathogen populations were similarly variable, with five out of 44 virulence phenotypes classified as common. Resistance and virulence structure were related to the occurrence of two distinct ecotypes of the host. Hill populations were consistently more resistant than those in bogs and their pathogen populations more virulent. Allozyme analysis showed a high degree of genetic differentiation between host ecotypes, with fixed allelic differences. Host and pathogen phenotypes were non‐randomly distributed between bog and hill sites. When ecotypic differences were factored out, there was clear evidence of a non‐random spatial distribution of resistance, with nearby populations being more likely to share resistance phenotypes, suggesting at least weak isolation by distance. While still apparent, this effect was much less noticeable in the pathogen populations, indicating significant differences in the spatial scale of dispersal of host and pathogen.