Salinization is a global phenomenon affecting ecosystems and forcing freshwater organisms to deal with increasing levels of ionic stress. However, our understanding of mechanisms that permit salt tolerance in amphibians is limited. This study investigates mechanisms of salt tolerance in locally adapted, coastal populations of a treefrog, Hyla cinerea. Using a common garden experiment, we (i) determine the extent that environment (i.e., embryonic and larval saltwater exposure) or genotype (i.e., coastal vs. inland) affects developmental benchmarks and transcriptome expression, and (ii) identify genes that may underpin differences in saltwater tolerance. Differences in gene expression, survival, and plasma osmolality were most strongly associated with genotype. Population genetic analyses on expressed genes also delineated coastal and inland groups based on genetic similarity. Coastal populations differentially expressed osmoregulatory genes including ion transporters (atp1b1, atp6V1g2, slc26a), cellular adhesion components (cdh26, cldn1, gjb3, ocln), and cytoskeletal components (odc1‐a, tgm3). Several of these genes are the same genes expressed by euryhaline fish after exposure to freshwater, which is a novel finding for North American amphibians and suggests that these genes may be associated with local salinity adaptation. Coastal populations also highly expressed glycerol‐3‐phosphate dehydrogenase 1 (gpd1), which indicates they use glycerol as a compatible osmolyte to reduce water loss – another mechanism of saltwater tolerance previously unknown in frogs. These data signify that Hyla cinerea inhabiting coastal, brackish wetlands have evolved a salt‐tolerant ecotype, and highlights novel candidate pathways that can lead to salt tolerance in freshwater organisms facing habitat salinization.

中文翻译：

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树蛙耐盐性局部适应的分子机制

盐碱化是一种影响生态系统并迫使淡水生物应对不断增加的离子胁迫的全球性现象。但是，我们对允许两栖动物耐盐的机制的理解是有限的。这项研究调查了本地适应的沿海蛙树蛙，Hyla cinerea的耐盐机制。使用常见的花园实验，我们（i）确定环境（即，胚胎和幼体盐水暴露）或基因型（即，沿海与内陆）对发展基准和转录组表达的影响程度，以及（ii）确定可能作为基础的基因耐盐水性的差异。基因表达，存活率和血浆渗透压的差异与基因型密切相关。对表达基因的群体遗传分析还根据遗传相似性来描绘沿海和内陆群体。沿海人口差异表达渗透调节基因，包括离子转运蛋白（atp1b1，atp6V1g2，slc26a），细胞粘附成分（cdh26，cldn1，gjb3，ocln）和细胞骨架成分（odc1‐a，tgm3）。这些基因中的几个与暴露于淡水后的淡水鱼表达的基因相同，这是北美两栖动物的新发现，表明这些基因可能与局部盐度适应有关。沿海人口还高表达甘油3磷酸脱氢酶1（gpd1），这表明他们使用甘油作为相容的渗透压降低水分流失-这是以前在青蛙中未知的耐盐水性的另一种机制。这些数据表明，Hyla cinerea 居住在沿海咸淡湿地上的人类已经发展了耐盐生态型，并着重指出了可能导致面临生境盐化的淡水生物耐盐性的新候选途径。