Data from: In absence of local adaptation, plasticity and spatially varying selection rule: a view from genomic reaction norms in a panmictic species (Anguilla rostrata)

Background: American eel (Anguilla rostrata) is one of the few species for which panmixia has been demonstrated at the scale of the entire species. As such, the development of long term local adaptation is impossible in this species. Instead, both plasticity and spatially varying selection have been invoked in explaining how American eel may cope with an unusual broad scope of environmental conditions. Here, we address this question through transcriptomic analyses and genomic reaction norms of eels from two geographic origins reared in controlled environments. Results: The null hypothesis of no difference of gene expression between eels from the two origins was rejected. Many unique transcripts and two out of seven gene clusters showed significant difference in expression, both at time of capture and after three months of common rearing. Differences in expression were observed at numerous genes representing many functional groups when comparing eels from a same origin reared in different salinity conditions. Plastic response to different rearing conditions varied among gene clusters with three clusters showing significant origin-environment interactions translating differential genomic norms of reaction. Most genes and functional categories showing differences between origins were previously shown to be differentially expressed in a study comparing transcription profiles between adult European eels acclimated to different salinities. Conclusions: These results emphasize that while plasticity in expression may be important, there is also a role for local genetic (and/or epigenetic) differences in explaining the extent of differences in gene expression between eels from different geographic origins. Such differences match those reported in genetically distinct populations in other fishes, both in terms of proportion of genes that are differentially expressed and the diversity of biological functions being involved. We thus propose that genetic differences between glass eels of different origins caused by spatially varying selection due to local environmental conditions translates into transcriptomic differences (including different genomic norms of reaction) which may in turn explain part of the phenotypic variance observed between different habitats colonized by eels.背景：美洲鳗鲡（Anguilla rostrata）是少数几种在整个物种种群尺度上被证实存在泛交（panmixia）的物种之一。因此，该物种无法形成长期的本地适应。为此，学界常借助表型可塑性以及空间异质性选择来解释美洲鳗鲡如何适应跨度极广的环境条件。本研究通过对两种地理起源的鳗鲡在可控环境下饲养后的转录组分析与基因组反应规范（genomic reaction norms）研究，探讨这一科学问题。 结果：本研究拒绝了“两种地理起源的鳗鲡基因表达无差异”的原假设。无论是在捕获时还是经过三个月的统一饲养后，均有大量独特转录本以及7个基因簇中的2个呈现出显著的表达差异。当比较同一地理起源、但饲养盐度不同的鳗鲡时，多个功能类群的大量基因均表现出表达差异。针对不同饲养环境的可塑性响应在各基因簇间存在差异，其中3个基因簇呈现出显著的起源-环境互作，对应着差异化的基因组反应规范。绝大多数存在起源差异的基因与功能类群，此前已有研究在比较不同盐度驯化的成年欧洲鳗鲡的转录谱时发现了类似的差异表达情况。 结论：本研究结果表明，尽管基因表达的可塑性可能发挥重要作用，但本地遗传（及/或表观遗传）差异同样可以解释不同地理起源鳗鲡间的基因表达差异。这类差异在差异表达基因的比例以及所涉及的生物学功能多样性上，均与其他鱼类中遗传分化种群的相关研究结果相符。据此我们提出：由本地环境条件引发的空间异质性选择所导致的不同地理起源玻璃鳗（glass eels）幼体间的遗传差异，会转化为转录组差异（包括差异化的基因组反应规范），这或许可以部分解释鳗鲡所定居的不同生境间观测到的表型变异。