Data from: Population structure of a vector-borne plant parasite

Parasites are among the most diverse groups of life on Earth, yet complex
natural histories often preclude studies of their speciation processes.
The biology of parasitic plants facilitates in situ collection of data on
both genetic structure and the mechanisms responsible for that structure.
Here, we studied the role of mating, dispersal and establishment in host
race formation of a parasitic plant. We investigated the population
genetics of a vector-borne desert mistletoe (Phoradendron californicum)
across two legume host tree species (Senegalia greggii and Prosopis
velutina) in the Sonoran desert using microsatellites. Consistent with
host race formation, we found strong host-associated genetic structure in
sympatry, little genetic variation due to geographic site and weak
isolation by distance. We hypothesize that genetic differentiation results
from differences in the timing of mistletoe flowering by host species, as
we found initial flowering date of individual mistletoes correlated with
genetic ancestry. Hybrids with intermediate ancestry were detected
genetically. Individuals likely resulting from recent, successful
establishment events following dispersal between the host species were
detected at frequencies similar to hybrids between host races. Therefore,
barriers to gene flow between the host races may have been stronger at
mating than at dispersal. We also found higher inbreeding and within-host
individual relatedness values for mistletoes on the more rare and isolated
host species (S. greggii). Our study spanned spatial scales to address how
interactions with both vectors and hosts influence parasitic plant
structure with implications for parasite virulence evolution and
speciation.