Department of Biological Sciences, Louisiana State University, Baton Rouge, LA 70803, USA.
Integr Comp Biol. 2019 Aug 1;59(2):306-319. doi: 10.1093/icb/icz035.
The eastern oyster, Crassostrea virginica, forms reefs that provide critical services to the surrounding ecosystem. These reefs are at risk from climate change, in part because altered rainfall patterns may amplify local fluctuations in salinity, impacting oyster recruitment, survival, and growth. As in other marine organisms, warming water temperatures might interact with these changes in salinity to synergistically influence oyster physiology. In this study, we used comparative transcriptomics, measurements of physiology, and a field assessment to investigate what phenotypic changes C. virginica uses to cope with combined temperature and salinity stress in the Gulf of Mexico. Oysters from a historically low salinity site (Sister Lake, LA) were exposed to fully crossed temperature (20°C and 30°C) and salinity (25, 15, and 7 PSU) treatments. Using comparative transcriptomics on oyster gill tissue, we identified a greater number of genes that were differentially expressed (DE) in response to low salinity at warmer temperatures. Functional enrichment analysis showed low overlap between genes DE in response to thermal stress compared with hypoosmotic stress and identified enrichment for gene ontologies associated with cell adhesion, transmembrane transport, and microtubule-based process. Experiments also showed that oysters changed their physiology at elevated temperatures and lowered salinity, with significantly increased respiration rates between 20°C and 30°C. However, despite the higher energetic demands, oysters did not increase their feeding rate. To investigate transcriptional differences between populations in situ, we collected gill tissue from three locations and two time points across the Louisiana Gulf coast and used quantitative PCR to measure the expression levels of seven target genes. We found an upregulation of genes that function in osmolyte transport, oxidative stress mediation, apoptosis, and protein synthesis at our low salinity site and sampling time point. In summary, oysters altered their phenotype more in response to low salinity at higher temperatures as evidenced by a higher number of DE genes during laboratory exposure, increased respiration (higher energetic demands), and in situ differential expression by season and location. These synergistic effects of hypoosmotic stress and increased temperature suggest that climate change will exacerbate the negative effects of low salinity exposure on eastern oysters.
东方牡蛎（Crassostrea virginica）形成的珊瑚礁为周围的生态系统提供了关键的服务。这些珊瑚礁面临着气候变化的威胁，部分原因是降雨量的变化可能会放大盐度的局部波动，从而影响牡蛎的繁殖、生存和生长。与其他海洋生物一样，水温升高可能会与盐度变化相互作用，协同影响牡蛎的生理机能。在这项研究中，我们使用比较转录组学、生理测量和实地评估来研究东方牡蛎在墨西哥湾中如何应对温度和盐度的综合胁迫。来自历史低盐度地点（路易斯安那州的姐妹湖）的牡蛎暴露于完全交叉的温度（20°C 和 30°C）和盐度（25、15 和 7 PSU）处理中。我们对牡蛎鳃组织进行比较转录组学分析，发现了更多在温暖条件下低盐度下差异表达（DE）的基因。功能富集分析显示，热应激和低渗胁迫下差异表达的基因之间的重叠较少，并且鉴定出与细胞黏附、跨膜转运和微管基过程相关的基因本体论富集。实验还表明，牡蛎在高温和低盐度下改变了它们的生理机能，在 20°C 和 30°C 之间呼吸率显著增加。然而，尽管能量需求增加，牡蛎并没有增加摄食率。为了研究现场种群之间的转录差异，我们在路易斯安那州墨西哥湾沿岸的三个地点和两个时间点采集了鳃组织，并使用定量 PCR 测量了七个靶基因的表达水平。我们发现，在低盐度地点和采样时间点，与渗透调节物转运、氧化应激调节、细胞凋亡和蛋白质合成相关的基因上调。总之，牡蛎在较高温度下对低盐度的反应更为明显，这表现在实验室暴露时差异表达的基因数量更多、呼吸作用增加（更高的能量需求）以及季节和地点的原位差异表达。这种低渗胁迫和温度升高的协同作用表明，气候变化将加剧低盐度暴露对东方牡蛎的负面影响。
