Genetic differentiation and estimated gene flow
A female gamete contributes both nuclear and cytoplasmic material, whereas a male gamete does not carry cytoplasmic material contrubuting to the formation of a zygote. When hybridization occurs between species, the nuclear genes of the offspring are a combined product of the different parental species, whereas the cytoplasmic genes of the offspring are contributed by their mother and are not recombinant (Greiner et al. 2015; Hagstrom et al. 2014). Thus, interspecies hybridization may lead to asymmetric genetic differentiation between nuclear and cytoplasmic material. There will be high genetic differentiation of nuclear genes but low genetic differentiation of cytoplasmic genes. Thus, we calculated the genetic differentiation of the termite species at the mitochondrial gene (COII) and nuclear gene (SSR) levels.F ST, a standardized measure of the genetic variance among populations, was calculated using GenAIEx v. 6.5, DnaSP v5 and FSTAT v. 2.9.3.2. Gene flow was indirectly measured using genetic frequency data.
To determine whether there was species-related genetic clustering of the populations of R. flaviceps, R. chinensis and their hybrid populations, we employed a Bayesian approach for inferring population structure using STRUCTURE 2.3. We ran the admixture model with correlated frequencies, with 10 independent runs for each K (from 1 to 10) performed with 10,000 MCMC repetitions and a burn-in of 10,000. We used the mean maximum estimated logarithm of the posterior probability of the data for each K (LnP(D)) to identify the most likely number of clusters, and we used DK values combined with species identification to obtain the optimal K.