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.

坎宁安南青冈（Nothofagus cunninghamii）是一类长寿的风媒传粉乔木，主导澳大利亚东南部的冷温带雨林群落。该物种在塔斯马尼亚州西部的分布大致连续，但在其余区域则呈片段化状态。目前尚不明确此类片段化是否会影响该物种的遗传架构（genetic architecture）。
为此，我们采用12对核微卫星（nuclear microsatellites）标记，对覆盖该物种自然分布范围的18个种群共633个个体开展了遗传分析。作为风媒传粉乔木的典型特征，该物种在整个分布范围内的遗传分化水平较低（固定指数FST=0.04），这与该物种多数分布区内存在显著基因流（gene flow）的结果相一致。但在部分地理隔离区域，基因流强度不足以抵消遗传漂变（genetic drift）带来的影响。
维多利亚州种群（与塔斯马尼亚州相隔宽达240公里的巴斯海峡）形成了一个与塔斯马尼亚州种群截然不同的遗传类群：其遗传多样性更低（维多利亚州平均等位基因丰富度(allelic richness, Ar)=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州种群（维多利亚州FST=0.045，塔斯马尼亚州为0.012）。
在距离其他种群至少20公里的小型种群中，检测到了种群瓶颈（population bottleneck）的相关证据。值得注意的是，我们发现在基于遗传的形态与生理海拔渐变群（altitudinal clines）两端的样本间，微卫星标记几乎未出现分化，这表明适应性分化主要由选择作用主导——因为此类分化很可能在存在基因流的情况下仍能发生。
尽管澳大利亚的冷温带雨林属于高度残遗的生态系统，但该物种凭借较高的遗传多样性与基因流水平，对种群片段化具有较强的耐受性，在塔斯马尼亚州尤为如此。