Studies of colonization of new habitats that appear from rapidly changing environments are interesting and highly relevant to our understanding of divergence and speciation. Here, we analyse phenotypic and genetic variation involved in the successful establishment of a marine fish (sand goby, Pomatoschistus minutus) over a steep salinity drop from 35 PSU in the North Sea (NE Atlantic) to two PSU in the inner parts of the post‐glacial Baltic Sea. We first show that populations are adapted to local salinity in a key reproductive trait, the proportion of motile sperm. Thereafter, we show that genome variation at 22,190 single nucleotide polymorphisms (SNPs) shows strong differentiation among populations along the gradient. Sequences containing outlier SNPs and transcriptome sequences, mapped to a draft genome, reveal associations with genes with relevant functions for adaptation in this environment but without overall evidence of functional enrichment. The many contigs involved suggest polygenic differentiation. We trace the origin of this differentiation using demographic modelling and find the most likely scenario is that at least part of the genetic differentiation is older than the Baltic Sea and is a result of isolation of two lineages prior to the current contact over the North Sea–Baltic Sea transition zone.

中文翻译：

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冰后在陡峭的盐度梯度上建立当地适应的鱼类种群

从快速变化的环境中出现的新栖息地的殖民化研究很有趣，并且与我们对分歧和物种形成的理解高度相关。在这里，我们分析了在盐度从北海（大西洋东北部）的 35 PSU 到帖子内部的两个 PSU 急剧下降的情况下成功建立海洋鱼类（沙虎鱼、Pomatoschistus minutus）所涉及的表型和遗传变异-冰川波罗的海。我们首先表明，种群在一个关键的生殖特征（活动精子的比例）中适应了当地的盐度。此后，我们表明 22,190 个单核苷酸多态性 (SNP) 的基因组变异显示出沿梯度的种群之间的强烈分化。包含离群 SNP 和转录组序列的序列，映射到基因组草图，揭示与在这种环境中具有适应相关功能的基因的关联，但没有功能丰富的总体证据。涉及的许多重叠群表明多基因分化。我们使用人口模型追踪这种分化的起源，发现最可能的情况是，至少部分遗传分化比波罗的海更古老，并且是在目前北海接触之前分离两个谱系的结果——波罗的海过渡区。