Data from: Genetic differentiation between two varieties of Oreocharis benthamii (Gesneriaceae) in sympatric and allopatric regions

The pattern of genetic differentiation between diverging species receives
much attention as one of the key observable features of speciation. It has
often been suggested that introgression between closely related species
occurs commonly where their distributions overlap, leading to their
becoming more morphologically and genetically similar, but there are a few
opposite results. However, most of these studies have been carried out
with animals and separate species; few have looked at intraspecific cases,
especially in plants. Here, we conduct a comparative study on patterns of
genetic differentiation among populations of two varieties of Oreocharis
benthamii in allopatry and sympatry based on ISSR data for 754 individuals
from 26 populations, in order to understand the processes leading to
speciation. Contrary to expectations, the facultative xenogamy (mixed
mating) species O. benthamii has a relatively low genetic diversity within
populations (H=0.1014, I=0.1528) and high genetic differentiation among
populations (GST=0.5867, ФST=0.659), as is typically found for selfing
species. Genetic variance between the two varieties in sympatric
populations (44%, ФST=0.444) is significantly more than that in allopatric
populations (14%, ФST=0.138). Consistent with the taxonomical delimitation
of the two varieties, all sampled individuals of O. benthamii clustered
into two genetic groups. Moreover, the genetic structures of populations
of both varieties is correlated with their different geographical origins.
Our studies show that significant divergence between sympatric populations
of the two varieties could be attributed primally to reinforcement by
genetic divergent selection in sympatry where secondary contact had
occurred. The major proportion of the genetic variation in outcrossing and
mixed mating plants may exist among populations when the populations are
distributed in fragmented habitats, due to the paucity of suitable habitat
combined with inefficient seed dispersal mechanism and limited pollinator
foraging area that may limit the gene flow.