Although Northern red oak (Quercus rubra L.) is the most important introduced deciduous tree species in Germany, only little is known about its genetic variation. For the first time, we describe patterns of neutral and potentially adaptive nuclear genetic variation in Northern red oak stands across Germany. For this purpose, 792 trees were genotyped including 611 trees from 12 stands in Germany of unknown origin and 181 trees from four populations within the natural distribution area in North America. Our marker set included 12 potentially adaptive (expressed sequence tag-derived simple sequence repeat = EST SSR) and 8 putatively selectively neutral nuclear microsatellite (nSSR) markers. Our results showed that German stands retain comparatively high levels of genetic variation at both EST-SSRs and nSSRs, but are more similar to each other than to North American populations. These findings are in agreement with earlier chloroplast DNA analyses which suggested that German populations originated from a limited geographic area in North America. The comparison between potentially adaptive and neutral microsatellite markers did not reveal differences in the analyzed diversity and differentiation measures for most markers. However, locus FIR013 was identified as a potential outlier locus. Due to the absence of signatures of selection in German stands, we suggest that introduced populations were established with material from provenances that were adapted to environmental conditions similar to those in Germany. However, we analyzed only a limited number of loci which are unlikely to be representative of adaptive genetic differences among German stands. Our results suggest that the apparent introduction from a limited geographic range in North America may go along with a reduced adaptive potential.

中文翻译：

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与北美种群相比，德国引进的红橡木（Quercus rubra）林分的遗传变异

尽管北方红橡树（Quercus rubra L.）是德国最重要的引进落叶树种，但对其遗传变异知之甚少。我们第一次描述了德国北部红橡树的中性和潜在适应性核遗传变异模式。为此，对 792 棵树进行了基因分型，其中包括来自德国 12 个未知来源林分的 611 棵树和来自北美自然分布区域内四个种群的 181 棵树。我们的标记集包括 12 个潜在的适应性（表达序列标签衍生的简单序列重复 = EST SSR）和 8 个推定的选择性中性核微卫星 (nSSR) 标记。我们的结果表明，德国林分在 EST-SSR 和 nSSR 上都保留了相对较高水平的遗传变异，但与北美人群相比，彼此更相似。这些发现与早期的叶绿体 DNA 分析一致，后者表明德国人口起源于北美有限的地理区域。潜在适应性和中性微卫星标记之间的比较并未揭示大多数标记分析的多样性和分化措施的差异。然而，基因座 FIR013 被确定为潜在的异常基因座。由于德国林分中没有选择的特征，我们建议引进的种群是用适应类似于德国环境条件的原产地材料建立的。然而，我们只分析了有限数量的基因座，这些基因座不太可能代表德国林分之间的适应性遗传差异。