Seawater carbonate chemistry and phenotypic Plasticity in Crassostrea virginica Larvae

Ocean acidification (OA) is a major threat to marine calcifiers, and little is known regarding acclimation to OA in bivalves. This study combined physiological assays with next-generation sequencing to assess the potential for recovery from and acclimation to OA in the eastern oyster (Crassostrea virginica) and identify molecular mechanisms associated with resilience. In a reciprocal transplant experiment, larvae transplanted from elevated pCO2 (~1400 ppm) to ambient pCO2 (~350 ppm) demonstrated significantly lower mortality and larger size post-transplant than oysters remaining under elevated pCO2 and had similar mortality compared to those remaining in ambient conditions. The recovery after transplantation to ambient conditions demonstrates the ability for larvae to rebound and suggests phenotypic plasticity and acclimation. Transcriptomic analysis supported this hypothesis as genes were differentially regulated under OA stress. Transcriptomic profiles of transplanted and non-transplanted larvae terminating in the same final pCO2 converged, further supporting the idea that acclimation underlies resilience. The functions of differentially expressed genes included cell differentiation, development, biomineralization, ion exchange, and immunity. Results suggest acclimation as a mode of resilience to OA. In addition, the identification of genes associated with resilience can serve as a valuable resource for the aquaculture industry, as these could enable marker-assisted selection of OA-resilient stocks.

海洋酸化（Ocean acidification, OA）是海洋钙化生物的主要威胁，而关于双壳类对OA的驯化机制，目前知之甚少。本研究结合生理测定与下一代测序（next-generation sequencing）技术，评估东部牡蛎（Crassostrea virginica）从OA胁迫中恢复及对OA驯化的潜力，并鉴定与韧性相关的分子机制。在互移植实验（reciprocal transplant experiment）中，将幼虫从高二氧化碳分压（partial pressure of carbon dioxide, pCO2，~1400 ppm）环境移植到自然二氧化碳分压（~350 ppm）环境后，其死亡率显著低于持续处于高pCO2环境的牡蛎，且体型更大；与持续处于自然环境的牡蛎相比，死亡率无显著差异。移植到自然环境后的恢复能力表明幼虫具有反弹潜力，并提示表型可塑性（phenotypic plasticity）与驯化机制的存在。转录组分析（transcriptomic analysis）支持这一假设，因为OA胁迫下基因表达存在差异调控。最终处于相同pCO2环境的移植组与非移植组幼虫的转录组谱趋于一致，进一步支持驯化是韧性基础的观点。差异表达基因的功能涉及细胞分化、发育、生物矿化（biomineralization）、离子交换及免疫等过程。研究结果表明，驯化是双壳类应对OA的一种韧性机制。此外，鉴定与韧性相关的基因可为水产养殖业提供宝贵资源，因为这些基因可用于OA韧性群体的标记辅助选择（marker-assisted selection）。