  The evergreen Quercus alnifolia and Q. coccifera form the only interfertile
pair of oak species growing in Cyprus. Hybridization between the two species
has already been observed and studied morphologically. However, little evidence
exists about the extent of genetic introgression. In the present study, we
aimed to study the effects of introgressive hybridization mutually on both
chloroplast and nuclear genomes. We sampled both pure and mixed populations of
Q. alnifolia and Q. coccifera from several locations across their distribution
area in Cyprus. We analyzed the genetic variation within and between species by
conducting Analysis of Molecular Variance (AMOVA) based on nuclear
microsatellites. Population genetic structure and levels of admixture were
studied by means of a Bayesian analysis (STRUCTURE simulation analysis).
Chloroplast DNA microsatellites were used for a spatial analysis of genetic
barriers. The main part of the nuclear genetic variation was explained by
partition into species groups. High interspecific differentiation and low
admixture of nuclear genomes, both in pure and mixed populations, support
limited genetic introgression between Q. alnifolia and Q. coccifera in Cyprus.
On the contrary, chloroplast DNA haplotypes were shared between the species and
were locally structured suggesting cytoplasmic introgression. Occasional
hybridization events followed by backcrossings with both parental species might
lead to this pattern of genetic differentiation.
