Patterns of genetic variation in native grape phylloxera on two sympatric host species.

Random amplified polymorphic DNA (RAPD) markers were used to examine population genetic structure in populations of native grape phylloxera. This research asked: (i) do RAPD markers distinguish two groups corresponding to the two host plant species; and (ii) do RAPD markers distinguish groups according to spatial location, independent of host plant association? Forty-nine phylloxera clones were collected from five pairs of adjacent individuals of two sympatric grape species in five sites along a 145 km transect in Missouri, USA. A high level of polymorphism was observed, with some evidence for structuring between host plant species and no evidence for spatial structuring. An analysis of molecular variance (AMOVA) found that 6.52% of the variance in RAPD banding patterns was attributable to host species and 7.96% of the variance was attributable to spatial location. A cluster analysis did not result in two groups corresponding to the two hosts, or to five groups corresponding to the geographical sites sampled. A Mantel test showed a low correlation between genetic similarity and spatial location. Two of the 93 RAPD markers were nonrandomly associated between the hosts. It is suggested that there may be a small host-mediated effect on genetic variation but stochastic dispersal and a highly heterogeneous environment may be the primary influences on the observed polymorphism.