Population Genetics And Species Divergence Of Pinus Massoniana And P. Hwangshanensis

Level of nucleotide polymorphism and degree of population differentiation are fundamental population genetics parameters that are strongly influenced by evolutionary forces that acted in the past. Their analysis can therefore be used to infer past demographic history and selection events. Pinus massoniana and P. hwangshanensis are two pine species with overlapping distributions in southeast China. However, these two species are different in morphology, cytology and wood anatomy. Here we investigated the nucleotide diversity, species divergence between these two species using sequences of twelve nuclear loci, by analysing samples from 22 wild populations across most of their distribution range. Both species exhibit low average value of nucleotide diversity across all 12 nucleotide loci, and the level of silent nucleotide diversity is two times higher in P. hwangshanensis(πsil= 0.0064,θwsil= 0.0062) than that in P. massoniana(πsil= 0.0033,θwsil= 0.0035). The lower nucleotide diversity in these Pine species could be best explained by their differences in the distributions and habitat preferences. Both species exhibit moderate levels of population differentiation (P. massoniana, FST= 0.289; P. hwangshanensis, FST 0.243) across all 12 nucleotide loci. Hierarchical AMOVA (Analysis of molecular variance) revealed that the average of variance components between species is 41.36% based on the 12 loci, and is significantly higher at locus GI (77.24%) than others. In addition, we constructed gene genealogies of each locus using the Median-Joining model by coalescent simulations, which demonstrated that shared haplotypes were observed in all loci except GI. Thus we speculate that GI (control flowering time) may have experienced the speciation-related selection, which further accelerated its lineage-sorting divergence between species.