1 Despite the recognition that spatial structure can have major consequence
s for the ecological and evolutionary dynamics of host-pathogen interaction
s, few empirical studies have examined how regional processes affect within
-population co-evolutionary patterns.
2 Considerable variation was detected within and among denies of a metapopu
lation in the resistance of Linum marginale to a range of local isolates of
the rust Melampsora lini. Only four resistance phenotypes were common (occ
urring at an overall frequency of > 5%) and pathogen populations were simil
arly variable, with five out of 44 virulence phenotypes classified as commo
3 Resistance and virulence structure were related to the occurrence of two
distinct ecotypes of the host. Hill populations were consistently more resi
stant than those in bogs and their pathogen populations more virulent. Allo
zyme 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.
4 When ecotypic differences were factored out, there was clear evidence of
a nonrandom spatial distribution of resistance, with nearby populations bei
ng more likely to share resistance phenotypes, suggesting at least weak iso
lation by distance. While still apparent, this effect was much less noticea
ble in the pathogen populations, indicating significant differences in the
spatial scale of dispersal of host and pathogen.