Data from: Genetic differentiation in spite of high gene flow in the dominant rainforest tree of southeastern Australia, Nothofagus cunninghamii

Nothofagus cunninghamii is a long-lived, wind-pollinated tree species that dominates the cool temperate rainforests of southeastern Australia. The species’ distribution is more or less continuous in western Tasmania but is fragmented elsewhere. However, it is unknown whether this fragmentation has affected the species’ genetic architecture. Thus, we examined N. cunninghamii using 12 nuclear microsatellites and 633 individuals from 18 populations spanning the species’ natural range. Typical of wind-pollinated trees, there was low range-wide genetic structure (FST=0.04) consistent with significant gene flow across most of the species’ range. However, gene flow was not high enough to overcome the effects of drift across some disjunctions. Victorian populations (separated from Tasmania by the 240 km wide Bass Strait) formed a genetic group distinct from Tasmanian populations, had lower diversity (mean allelic richness (Ar)=5.4 in Victoria versus 6.9 in Tasmania) and were significantly more differentiated from one another than those in Tasmania (FST=0.045 in Victoria versus 0.012 in Tasmania). Evidence for bottlenecking was found in small populations that were at least 20 km from other populations. Interestingly, we found little divergence in microsatellite markers between the extremes of genetically based morphological and physiological altitudinal clines suggesting adaptive differentiation is strongly driven by selection because it is likely to be occurring in the presence of gene flow. Even though the cool temperate rainforests of Australia are highly relictual, the species is relatively robust to population fragmentation due to high levels of genetic diversity and gene flow, especially in Tasmania.坎宁安假山毛榉（Nothofagus cunninghamii）是一种长寿的风媒传粉乔木物种，为澳大利亚东南部寒温带雨林的优势树种。该物种的分布格局在塔斯马尼亚州西部大致连续，但在其余区域呈现碎片化特征。目前尚不明确这种生境破碎化是否会对该物种的遗传结构造成影响。 为此，研究团队采用12个核微卫星（nuclear microsatellites）标记，对覆盖该物种自然分布范围的18个种群的633个个体开展了遗传分析。与风媒传粉乔木的典型特征相符，该物种在全域范围内的遗传分化程度整体偏低（群体分化系数FST=0.04），这与物种多数分布区内存在显著基因流的结果相契合。然而，部分地理隔离区域的基因流强度尚未高到足以抵消遗传漂变的效应。 维多利亚州种群与塔斯马尼亚州种群被宽240公里的巴斯海峡（Bass Strait）分隔，二者形成了显著分化的遗传类群；维多利亚州种群的遗传多样性更低（平均等位基因丰富度（Ar）为5.4，塔斯马尼亚州为6.9），且种群间的遗传分化程度显著高于塔斯马尼亚种群（维多利亚州FST=0.045，塔斯马尼亚州FST=0.012）。 在距离其他种群至少20公里的小型种群中，研究人员检测到了种群瓶颈效应的相关证据。值得注意的是，在基于遗传的形态与生理海拔梯度的极端类群间，仅观察到极微弱的微卫星标记分化，这表明适应性分化主要由选择作用驱动——因为这类分化很可能在存在基因流的背景下发生。 尽管澳大利亚的寒温带雨林属于高度残遗的生态系统，但该物种凭借高水平的遗传多样性与基因流（尤其是在塔斯马尼亚州境内），对种群碎片化具备较强的耐受能力。