马尾松和黄山松两个核基因位点的群体遗传多样性和种间分化

Population genetic diversity and species divergence of Pinus massoniana and P.hwang-shanensis at two nucleotide loci

利用两个核基因座位C3H和GI,对重叠分布于中国东南部的两个松属(Pinus)物种马尾松(P.massoniana)和黄山松(P.hwangshanensis)的22个群体88个个体进行了遗传多样性和种间分化模式研究。在这两个核基因座位上,两种植物都表现出较低的核苷酸多样性水平(马尾松πsil=0.00171;黄山松πsil=0.00340),但是马尾松要显著低于黄山松;在种内分化水平上,马尾松的种内遗传分化也明显低于黄山松(马尾松FST=0.059;黄山松FST=0.339)。这可能是由于黄山松的海拔分布高于马尾松,而高海拔分布使黄山松的分布区域更加片段化,促使其形成较高的种内遗传多样性和遗传分化。分子变异分析(AMOVA)发现,两物种基于两个核基因座位的种间差异为48.86%,而GI基因座位上的种间差异明显高于C3H座位(GI:77.24%,C3H:20.48%),同时,基因谱系显示两物种的共享单倍型仅在C3H座位上存在。结合这两个基因的功能,推测GI基因可能在物种形成过程中受到了一定的选择压力,因为GI基因参与调控植物的开花时间,而C3H与木质素表达水平的调控有关。不同的选择压力使得GI的进化速度相对较快,从而加速了黄山松和马尾松的物种分化。

Aims Our objective was to examine population genetic diversity and species divergence of two pine species （Pinus massoniana and P. hwangshanensis） with overlapping distributions in southeastern China. Methods We estimated levels of nucleotide diversity and an analysis of molecular variance （AMOVA） of the two species based on sequence data of two nuclear loci for 88 individuals from 22 populations of the two species across most of their range of distribution. Gene genealogies of each locus were constructed by coalescent simulations using the Median-Joining model. Important findings Both species exhibit low levels of nucleotide diversity at two nucleotide loci, and the level of silent nucleotide diversity is two times higher in P. hwangshanensis （πsil = 0.003 40） than that in P massoniana （πsil= 0.001 71）. The population differentiation （FST is also significantly different between the two species （P massoniana, 0.059; P. hwangshanensis, 0.339, p 〈 0.05）. These genetic differences in the population structure of the two species may result from their differences in distribution and habitat preference. Hierarchical AMOVA revealed that the average of variance components between species is 48.86% based on the two loci and is significantly higher at locus G1 （77.24%） than locus C3H （20.48%）. In addition, shared haplotypes were only observed in C3H rather than GI. Thus we speculate that G1 （control of flowering time） may have experienced speciation-related selection, which further accelerated its lineage-sorting divergence between the species.