Environmental variation along the geographical space can shape populations by natural selection. In the context of global warming and changing precipitation regimes, it is crucial to understand the role of environmental heterogeneity in tropical trees adaptation, given their disproportional contribution to water and carbon biogeochemical cycles. Here, we investigated how heterogeneity in freshwater availability along tropical wetlands has influenced molecular variations of the black mangrove (Avicennia germinans). A total of 57 trees were sampled at seven sites differing markedly in precipitation regime and riverine freshwater inputs. Using 2,297 genome-wide single nucleotide polymorphic markers, we found signatures of natural selection by the association between variations in allele frequencies and environmental variables, including the precipitation of the warmest quarter and the annual precipitation. Additionally, we found candidate loci for selection based on statistical deviations from neutral expectations of interpopulation differentiation. Most candidate loci within transcribed sequences were functionally associated with central aspects of drought tolerance or plant response to drought. Moreover, our results suggest the occurrence of the rapid evolution of a population, probably in response to sudden and persistent limitations in plant access to soil water, following a road construction in 1974. Observations supporting rapid evolution included the reduction in tree size and changes in allele frequencies and in transcript expression associated with increased drought tolerance through the accumulation of osmoprotectants and antioxidants, biosynthesis of cuticles, protection against protein degradation, stomatal closure, photorespiration and photosynthesis. We describe a major role of spatial heterogeneity in freshwater availability in the specialization of this typically tropical tree.

中文翻译：

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红树林树Avicennia Germinans（Acanthaceae）对淡水限制的分子响应。

地理空间中的环境变化可以通过自然选择来塑造种群。在全球变暖和降水变化的背景下，了解环境异质性对热带树木适应的作用至关重要，因为热带树木对水和碳生物地球化学循环的贡献不成比例。在这里，我们调查了沿热带湿地的淡水可利用性的异质性如何影响黑红树林（Avicennia Germinans）的分子变异。在七个地点的总共57棵树被采样，这两个地区的降水方式和河流淡水输入量明显不同。使用2,297个全基因组范围的单核苷酸多态性标记，我们通过等位基因频率变化与环境变量之间的关联发现了自然选择的特征，包括最暖季的降水量和年降水量。此外，我们根据与群体间分化的中性预期之间的统计偏差找到了可供选择的候选基因座。转录序列中的大多数候选基因座在功能上与干旱耐受性或植物对干旱的反应的主要方面有关。此外，我们的研究结果表明，人口快速进化的发生可能是由于1974年修路后植物获得土壤水的突然和持续的限制所致。通过渗透保护剂和抗氧化剂的积累，与提高的耐旱性相关的等位基因频率和转录本表达，角质层的生物合成，防止蛋白质降解，气孔关闭，光呼吸和光合作用。我们在这种典型的热带树木的专业化中描述了空间异质性在淡水可利用性中的主要作用。