Genomic variation within and among populations is shaped by the interplay between natural selection and the effects of genetic drift and gene flow. Adaptive divergence can be found in small-scale natural systems even when population sizes are small, and the potential for gene flow is high, suggesting that local environments exert selection pressures strong enough to counteract the opposing effects of drift and gene flow. Here, we investigated genomic differentiation in nine moor frog (Rana arvalis) populations in a small-scale network of local wetlands using 16,707 ddRAD-seq SNPs, relating levels of differentiation with local environments, as well as with properties of the surrounding landscape. We characterized population structure and differentiation, and partitioned the effects of geographic distance, local larval environment, and landscape features on total genomic variation. We also conducted gene-environment association studies using univariate and multivariate approaches. We found small-scale population structure corresponding to 6-8 clusters. Local larval environment was the most influential component explaining 2.3% of the total genetic variation followed by landscape features (1.8%) and geographic distance (0.8%), indicative of isolation-by-environment, -by-landscape, and -by-distance, respectively. We identified 1000 potential candidate SNPs putatively under divergent selection mediated by the local larval environment. The candidate SNPs were involved in, among other biological functions, immune system function and development. Our results suggest that small-scale environmental differences can exert selection pressures strong enough to counteract homogenizing effects of gene flow and drift in this small-scale system, leading to observable population differentiation.

中文翻译：

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小规模种群分化是由温带两栖动物的当地幼虫环境驱动的

种群内部和种群之间的基因组变异是由自然选择与遗传漂变和基因流动的影响之间的相互作用形成的。即使种群规模很小，并且基因流动的潜力很高，也可以在小规模自然系统中发现适应性分歧，这表明当地环境施加的选择压力足以抵消漂移和基因流动的相反影响。在这里，我们使用 16,707 个 ddRAD-seq SNP 研究了当地湿地小规模网络中 9 种沼泽蛙 (Rana arvalis) 种群的基因组分化，将分化水平与当地环境以及周围景观的特性相关联。我们描述了种群结构和分化，划分了地理距离、当地幼虫环境、和总基因组变异的景观特征。我们还使用单变量和多变量方法进行了基因-环境关联研究。我们发现了对应于 6-8 个集群的小规模人口结构。当地的幼虫环境是最有影响力的成分，占总遗传变异的 2.3%，其次是景观特征 (1.8%) 和地理距离 (0.8%)，表明环境隔离、景观隔离和距离隔离， 分别。我们在由当地幼虫环境介导的不同选择下推定了 1000 个潜在的候选 SNP。除其他生物学功能外，候选单核苷酸多态性参与免疫系统功能和发育。