The Swire Institute of Marine Science and School of Biological Sciences, University of Hong Kong, Pokfulam, Hong Kong Special Administrative Region, China.
School of Aquatic and Fishery Sciences, University of Washington, 1122, NE Boat Street, Seattle, WA, USA.
Mar Environ Res. 2021 Jan;163:105217. doi: 10.1016/j.marenvres.2020.105217. Epub 2020 Nov 25.
Unprecedented rate of increased CO level in the ocean and the subsequent changes in carbonate system including decreased pH, known as ocean acidification (OA), is predicted to disrupt not only the calcification process but also several other physiological and developmental processes in a variety of marine organisms, including edible oysters. Nonetheless, not all species are vulnerable to those OA threats, e.g. some species may be able to cope with OA stress using environmentally induced modifications on gene and protein expressions. For example, external environmental stressors including OA can influence the addition and removal of methyl groups through epigenetic modification (e.g. DNA methylation) process to turn gene expression "on or off" as part of a rapid adaptive mechanism to cope with OA. In this study, we tested the above hypothesis through testing the effect of OA, using decreased pH 7.4 as proxy, on DNA methylation pattern of an endemic and a commercially important estuary oyster species, Crassostrea hongkongensis at the time of larval habitat selection and metamorphosis. Larval growth rate did not differ between control pH 8.1 and treatment pH 7.4. The metamorphosis rate of the pediveliger larvae was higher at pH 7.4 than those in control pH 8.1, however over one-third of the larvae raised at pH 7.4 failed to attach on optimal substrate as defined by biofilm presence. During larval development, a total of 130 genes were differentially methylated across the two treatments. The differential methylation in the larval genes may have partially accounted for the higher metamorphosis success rate under decreased pH 7.4 but with poor substratum selection ability. Differentially methylated loci were concentrated in the exon regions and appear to be associated with cytoskeletal and signal transduction, oxidative stress, metabolic processes, and larval metamorphosis, which implies the high potential of C. hongkongensis larvae to acclimate and adapt through non-genetic ways to OA threats within a single generation.
海洋中二氧化碳（CO）水平的空前增长以及随之而来的碳酸盐体系变化，包括 pH 值降低，即海洋酸化（OA），预计不仅会破坏钙化过程，还会干扰多种海洋生物的其他生理和发育过程，包括可食用的牡蛎。然而，并非所有物种都容易受到 OA 威胁，例如，一些物种可能能够通过基因和蛋白质表达的环境诱导变化来应对 OA 压力。例如，外部环境胁迫因素包括 OA，可以通过表观遗传修饰（例如 DNA 甲基化）过程影响甲基的添加和去除，从而将基因表达“开启或关闭”，作为应对 OA 的快速适应机制的一部分。在这项研究中，我们通过测试 OA 的影响，使用降低的 pH 值 7.4 作为代理，来测试一种特有和一种商业上重要的河口牡蛎物种 Crassostrea hongkongensis 在幼虫栖息地选择和变态时期的 DNA 甲基化模式。在对照 pH 值 8.1 和处理 pH 值 7.4 下，幼虫的生长速度没有差异。在 pH 值 7.4 下，幼体牡蛎幼虫的变态率高于对照 pH 值 8.1 下的变态率，然而，超过三分之一在 pH 值 7.4 下饲养的幼虫未能附着在最佳基质上，最佳基质由生物膜存在定义。在幼虫发育过程中，两种处理方式共检测到 130 个差异甲基化基因。幼虫基因中的差异甲基化可能部分解释了在 pH 值 7.4 降低的情况下较高的变态成功率，但选择最佳基质的能力较差。差异甲基化的基因座集中在外显子区域，似乎与细胞骨架和信号转导、氧化应激、代谢过程和幼虫变态有关，这意味着 C. hongkongensis 幼虫具有通过非遗传方式适应 OA 威胁的高潜力，在单一代内即可适应和适应。
