Genetic differentiation and gene flow
Based on the mitochondrial and nuclear genetic results, the genetic differentiation between the two species was calculated using F-statistics (Table 2). We found that R. flaviceps and R. chinensis displayed asymmetric genetic differentiation between their mitochondrial and nuclear genes (t = 10.72, p < 0.001). The mtDNA COII gene analysis showed high genetic divergence and low gene flow between the species (F st> 0.62, N m < 0.15, Table 2), but the nuclear genes (SSRs) showed low genetic divergence and high gene flow between the species (F st< 0.12, N m > 2.63, Table 2). The asymmetric genetic differentiation between the nuclear and cytoplasmic material indicated that there was interspecific hybridization between R. flaviceps and R. chinensis.
Nuclear introgression from either R. flaviceps into R. chinensis or R. chinensis into R. flaviceps was unconstrained in the sympatric area. Among 38 colonies possessing R.flaviceps mtDNA haplotypes, anR. chinensis -specific nuclear haplotype was observed at proportions ranging from 1.5% (Wuhan) to 23.7% (Chengdu), with a mean of 10% (Table 3). Similarly, in 29 colonies possessing R. chinensis mtDNA haplotypes, a R. flaviceps -specific nuclear haplotype was found at proportions ranging from 2.2% (Wuhan) to 14.9% (Chengdu), with a mean of 6% in the colonies on a genetic basis. In other words, approximately 10% of female individuals of R. flaviceps mated with males of R. chinensis, and approximately 6% of female individuals of R. chinensis mated with males of