Evolutionary responses to ocean acidification in free-living protists.

虽然在日益酸化的海洋中影响生存的许多严重后果已经引起了人们的极大关注，特别是对钙化生物的生理影响，但我们还没有意识到这种选择压力的长期进化反应及其对种内生物多样性的伴随影响。这是我们知识中的一个严重缺口，因为生物多样性在种群可持续性中发挥着关键作用，从而影响到生态系统的功能。为了解决这个问题，我们提出了一个海洋原生动物模型的实验方法，因为这个分类群生长迅速，具有生态重要性，分布广泛，貌似似是而非，并且占据了一系列的环境。具体地说，我们选择了异养鞭毛藻Oxyrris marina，因为它分布广泛，易于培养，其生长速度受到pH条件的影响，尽管不同菌株的特定生理反应有所不同。通过对来自世界各地海洋栖息地的一系列不同(遗传和生态生理学)滨海奥里纳细菌进行一系列实验，我们的目标是确定(1)海洋酸化对种内多样性和种群结构模式的未来影响，以及(2)确定未来气候情景是否存在可预测的结果。具体地说，我们问：1.对酸化的响应，海洋假单胞菌菌株之间的生态生理差异有多大？2.跨越酸度梯度的进化结果是否可以从菌株的生态生理特征中预测？3.系统的复杂性是否影响决定论的程度？4.酸化速率是否影响海洋假单胞菌的酸化能力，从而影响进化的结果？我们首先刻画了海洋假单胞菌生长速率的生态生理变化谱，以开发预测它们在不同海洋酸度下的竞争能力的模型。此外，菌株之间的遗传差异水平将被量化，并用于确定对pH的反应是否具有明显的系统地理成分。接下来，我们研究这样一种情景，即随着酸度的增加，选择可能会更强，对选择的反应更具确定性/可预测性。因此，对pH具有不同生长反应的菌株之间的竞争结果将被追溯到100-200代，以揭示“随时间进化”的进程。这些实验的数据将与不同PHS下的增长率预测模型进行比较，从而确定对选择的反应是可预测的还是随机的。此外，我们目前的工作揭示了北大西洋(低多样性)和地中海(高多样性)之间的生物多样性二分法，这可能会影响这两个区域对环境变化的整体反应。为了确定遗传多样性(种群复杂性)是否影响选择结果，我们将在单一pH下进行另一项长期(100-200代)选择实验，选择建立在不同遗传变异水平上的重复种群。这个实验确定了菌株之间的竞争结果是否随着种群多样性的不同而不同，以及当有更大的长期遗传变异供选择采取行动时，对选择的反应是否更强。最后，我们假设，快速变化将比缓慢变化产生更大的影响，这可能会使菌株适应环境。因此，我们将比较多达10个不同菌株在一系列驯化期的处理反应。这些实验将不仅揭示海洋酸化的直接影响，而且揭示这种公认的气候变化压力对海洋生命进化的潜在后果，从而揭示我们的海洋对不可避免的变化的适应能力。

While many gross consequences that impact upon survival in an increasingly acidified ocean have attracted much attention, particularly, for example, the physiological effects upon calcifying organisms, we have yet to appreciate the long-term evolutionary response to this selective pressure and its concomitant effect on intraspecific biodiversity. This is a critical gap in our knowledge as biodiversity plays a key role in population persistence and thus affects ecosystem function. To address this issue, we propose an experimental approach on a model marine protist since this taxon is fast-growing, ecologically important, widespread, specious and occupies a range of environments. Specifically, we have selected the heterotrophic flagellate Oxyrrhis marina as it is widespread and easy to culture, and its growth rate is affected by pH conditions, although the specific physiological response varies among strains. Using a series of experiments on a bank of diverse (genetically and ecophysiologically) O.marina cultures sourced from habitats across the World's oceans, we aim to determine (1) the future consequences of ocean-acidification on patterns of intraspecific diversity and population structure and (2) identify whether there is a predictable outcome to future climate scenarios. Specifically we ask: 1. What is the extent of ecophysiological variation among O.marina-strains in response to acidification? 2. Is the outcome of evolution across an acidity gradient predictable from the ecophysiological profiles of strains? 3. Does system complexity affect the degree of determinism? 4. Does the rate of acidification affect the ability of O.marina to acclimate and thus impact on the outcome of evolution? We first characterise the spectrum of ecophysiological variation in growth rates in O.marina isolates to develop predictive models about their competitive ability under different ocean acidities. In addition, the level of genetic differences between strains will be quantified and used to determine whether response to pH has a distinct phylogeographic component. Next, we examine the scenario that selection is likely to be stronger, and the response to selection more deterministic/predictable, as acidity increases. Thus, the outcome of competition between strains with different growth responses to pH over 100-200 generations will be back-tracked to reveal the progress of 'evolution through time'. Data from these experiments will be compared to the predictive model of growth rates under different pHs, thus determining whether response to selection is predictable or stochastic. In addition, our current work reveals a dichotomy in biodiversity between the North Atlantic (low diversity) and the Mediterranean (high diversity) which may impact on the regions' overall response to environment change. To determine whether genetic diversity (population complexity) impacts upon the outcome of selection we will run another long-term (100-200 generation) selection experiment at a single pH with replicate populations founded with different levels of standing genetic variation. This experiment determines whether the outcome of competition between strains varies with population diversity, and whether the response to selection is stronger when there is greater standing genetic variation for select for selection to act upon. Finally we hypothesise that rapid changes will have greater impact than slow changes, which may allow strains to acclimate. Therefore, we will compare the responses of treatments of up to 10 divergent strains across a range of acclimation periods. Together these experiments will reveal not simply the immediate impact of ocean acidification but the potential consequences of this well accepted climate-change pressure on the evolution of life in the oceans, and thus the adaptability of our oceans to inevitable change.