Seawater carbonate chemistry and growth rate of Emiliania huxleyi in lab experiment@en

Predicting the impacts of environmental change on marine organisms, food webs, and biogeochemical cycles presently relies almost exclusively on short-term physiological studies, while the possibility of adaptive evolution is often ignored. Here, we assess adaptive evolution in the coccolithophore Emiliania huxleyi, a well-established model species in biological oceanography, in response to ocean acidification. We previously demonstrated that this globally important marine phytoplankton species adapts within 500 generations to elevated CO2. After 750 and 1000 generations, no further fitness increase occurred, and we observed phenotypic convergence between replicate populations. We then exposed adapted populations to two novel environments to investigate whether or not the underlying basis for high CO2-adaptation involves functional genetic divergence, assuming that different novel mutations become apparent via divergent pleiotropic effects. The novel environment \"high light\" did not reveal such genetic divergence whereas growth in a low-salinity environment revealed strong pleiotropic effects in high CO2 adapted populations, indicating divergent genetic bases for adaptation to high CO2. This suggests that pleiotropy plays an important role in adaptation of natural E. huxleyi populations to ocean acidification. Our study highlights the potential mutual benefits for oceanography and evolutionary biology of using ecologically important marine phytoplankton for microbial evolution experiments.

当前，预测环境变化对海洋生物、食物网及生物地球化学循环的影响几乎完全依赖短期生理学研究，而适应性进化的可能性常被忽视。本研究针对海洋酸化胁迫，对生物海洋学领域公认的模式物种——赫氏颗石藻（Emiliania huxleyi，隶属于颗石藻（coccolithophore）类群）的适应性进化展开评估。此前我们已证实，这一全球重要的海洋浮游植物物种可在500代内适应高CO₂环境。当培养至750代与1000代时，未再观测到适合度（fitness）提升，且重复种群间出现了表型趋同现象。随后我们将适应性种群暴露于两种全新环境，以探究高CO₂适应性的内在基础是否涉及功能遗传分化；本研究的假设前提为：不同的新发突变可通过差异化的多效性（pleiotropy）效应得以显现。‘高光强’这一全新环境未显现出此类遗传分化，而低盐度环境下的生长实验则在高CO₂适应性种群中观测到了显著的多效性效应，表明高CO₂适应性的遗传基础存在分化。上述结果表明，多效性在自然赫氏颗石藻种群适应海洋酸化的过程中发挥着重要作用。本研究凸显了利用具有重要生态意义的海洋浮游植物开展微生物进化实验，对海洋学与进化生物学研究的潜在双向增益价值。