Department of Biology & CESAM, University of Aveiro, Campus de Santiago, 3810-193 Aveiro, Portugal.
CFE - Centre for Functional Ecology, Department of Life Sciences, University of Coimbra, Calçada Martim de Freitas, 3000-456 Coimbra, Portugal.
Sci Total Environ. 2018 Apr 1;619-620:194-202. doi: 10.1016/j.scitotenv.2017.11.094. Epub 2017 Nov 29.
Sea level rise, as a consequence of climate changes, is already causing seawater intrusion in some freshwater coastal ecosystems worldwide. The increase in salinity at these freshwater coastal ecosystems may occur gradually (through groundwater) or abruptly (through extreme weather events). Moreover, many of them are also being altered and threatened by anthropogenic activities. Accordingly, the present study aimed at assessing the multigenerational lethal and sublethal effects caused by increased salinity in six clonal lineages of the freshwater cladoceran Daphnia longispina differing in their sensitivity to lethal levels of copper. Three specific objectives were delineated: i) to compare the lethal and sublethal toxicity of sodium chloride (NaCl) and natural seawater (SW); ii) to evaluate possible multigenerational effects after exposure to low levels of salinity, and iii) to evaluate if an association exists between tolerance to lethal and sublethal levels of salinity and tolerance to metals. Overall, NaCl was found to elicit sublethal effects at lower or similar concentrations than SW, suggesting its use as a protective surrogate of SW in early phases of ecological risk assessment schemes. Multigenerational exposure to conductivities of 0.73±0.015mScm led to dissimilar responses by the six clonal lineages. Significant associations were found neither between lethal and sublethal endpoints nor between salinity and metals, possibly indicating the absence of common mechanisms responsible to confer metal tolerance and salt stress. However, some clonal lineages presented an inverse sensitivity to lethal levels of NaCl and of copper. These results suggest that natural populations of D. longispina, by exhibiting clonal lineages with differential tolerance to increased salinity, may cope with long-term exposure to small increases of this stressor. However, over time those populations may face the occurrence of genetic erosion due to the loss of the most sensitive genotypes before or after a multigenerational exposure.
海平面上升是气候变化的后果，已经导致全球一些淡水沿海生态系统发生海水入侵。这些淡水沿海生态系统的盐度增加可能是逐渐的（通过地下水）或突然的（通过极端天气事件）。此外，许多生态系统还受到人为活动的改变和威胁。因此，本研究旨在评估 6 个淡水枝角类动物 Daphnia longispina 克隆系在不同铜致死水平下对盐度增加的多代致死和亚致死效应，这些克隆系对盐度增加的敏感性不同。确定了三个具体目标：i）比较氯化钠（NaCl）和天然海水（SW）的致死和亚致死毒性；ii）评估在低水平盐度暴露后的可能多代效应；iii）评估对致死和亚致死盐度水平的耐受性与对金属的耐受性之间是否存在关联。总的来说，发现 NaCl 在比 SW 低或相似浓度下产生亚致死效应，表明它可作为生态风险评估方案早期阶段 SW 的保护性替代物。对电导率为 0.73±0.015mScm 的多代暴露导致 6 个克隆系产生不同的反应。在致死和亚致死终点之间以及在盐度和金属之间均未发现显著关联，这可能表明不存在负责赋予金属耐受性和盐胁迫的共同机制。然而，一些克隆系对 NaCl 和铜的致死水平表现出相反的敏感性。这些结果表明，D. longispina 的自然种群通过表现出对增加盐度具有不同耐受性的克隆系，可能能够应对这种胁迫因素的长期小幅度增加。然而，随着时间的推移，由于在多代暴露前后丧失最敏感的基因型，这些种群可能会面临遗传侵蚀的发生。
