Astrangia poculata is a temperate scleractinian coral that exists in facultative symbiosis with the dinoflagellate alga Breviolum psygmophilum across a range spanning the Gulf of Mexico to Cape Cod, Massachusetts. Our previous work on metabolic thermal performance of Virginia (VA) and Rhode Island (RI) populations of A. poculata revealed physiological signatures of cold (RI) and warm (VA) adaptation of these populations to their respective local thermal environments. Here, we used whole-transcriptome sequencing (mRNA-Seq) to evaluate genetic differences and identify potential loci involved in the adaptive signature of VA and RI populations. Sequencing data from 40 A. poculata individuals, including 10 colonies from each population and symbiotic state (VA-white, VA-brown, RI-white, and RI-brown), yielded a total of 1,808 host-associated and 59 algal symbiont-associated single nucleotide polymorphisms (SNPs) post filtration. Fst outlier analysis identified 66 putative high outlier SNPs in the coral host and 4 in the algal symbiont. Differentiation of VA and RI populations in the coral host was driven by putatively adaptive loci, not neutral divergence (Fst = 0.16, p = 0.001 and Fst = 0.002, p = 0.269 for outlier and neutral SNPs respectively). In contrast, we found evidence of neutral population differentiation in B. psygmophilum (Fst = 0.093, p = 0.001). Several putatively adaptive host loci occur on genes previously associated with the coral stress response. In the symbiont, three of four putatively adaptive loci are associated with photosystem proteins. The opposing pattern of neutral differentiation in B. psygmophilum, but not the A. poculata host, reflects the contrasting dynamics of coral host and algal symbiont population connectivity, dispersal, and gene by environment interactions.

中文翻译：

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美国中大西洋沿岸温带珊瑚 Astrangia poculata 中的适应性发散、中性 panmixia 和藻类共生体种群结构

Astrangia poculata 是一种温带的硬骨珊瑚，在墨西哥湾到马萨诸塞州科德角的范围内与甲藻存在共生关系。我们之前对 A. poculata 的弗吉尼亚 (VA) 和罗德岛 (RI) 种群代谢热性能的研究揭示了这些种群对各自局部热环境的冷 (RI) 和暖 (VA) 适应的生理特征。在这里，我们使用全转录组测序（mRNA-Seq）来评估遗传差异并确定参与 VA 和 RI 群体适应性特征的潜在位点。来自 40 个 A. poculata 个体的测序数据，包括来自每个种群和共生状态（VA-white、VA-brown、RI-white 和 RI-brown）的 10 个菌落，总共产生了 1、过滤后的 808 个宿主相关和 59 个藻类共生体相关的单核苷酸多态性 (SNP)。第一次异常值分析在珊瑚宿主中确定了 66 个假定的高异常值 SNP，在藻类共生体中确定了 4 个。珊瑚宿主中 VA 和 RI 种群的分化是由假定的适应性位点驱动的，而不是中性发散（Fst = 0.16，p = 0.001 和 Fst = 0.002，p = 0.269 分别对于异常值和中性 SNP）。相比之下，我们在 B. psygmophilum 中发现了中性种群分化的证据（Fst = 0.093，p = 0.001）。几个假定的适应性宿主基因座出现在先前与珊瑚应激反应相关的基因上。在共生体中，四个假定的适应性位点中的三个与光系统蛋白相关。B. psygmophilum 中性分化的相反模式，而不是 A. poculata 宿主，