1. Salt pollution of freshwater ecosystems represents a major threat to biodiversity, and particularly to interactions between free‐living species and their associated parasites. Acanthocephalan parasites are able to alter their intermediate host's phenotype to reach final hosts, but this process could be affected by salt pollution, thereby compromising survival of the parasite.
2. We experimentally assessed the impact of salt on the extended phenotype of the parasite Pomphorhynchus laevis in their intermediate host, the amphipod Gammarus pulex, based on three amphipod behaviours: distance covered in flowing water, phototaxis, and geotaxis. We hypothesised that: (1) salt pollution negatively affected the behaviour of uninfected gammarids, and (2) that P. laevis could maintain their capacity to manipulate their host despite this pollution.
3. All three amphipod behaviours were altered by P. laevis: infected G. pulex covered a greater distance, were less photophobic and were more attracted to the water surface than uninfected amphipods, in control or salt‐polluted water. However, salinity reduced distance covered in flowing water and increased attraction to the water surface of uninfected and infected G. pulex. For the phototaxis behaviour, P. laevis enhanced this capacity of manipulation in salt‐polluted water compared to control water.
4. Pomphorhynchus laevis can still manipulate the behaviour of their intermediate host in salt‐polluted water. Acanthocephalan parasites have not been known to be able to manipulate their intermediate host when under pollution stress. Trophic interactions, but not the chances of parasite transmission to their definitive host, appear to be affected by salt pollution.
5. Our study indicates that behavioural modifications induced by complex lifecycle parasites should be more considered in the context of growing concentrations of chemical pollutants in some freshwater ecosystems. Interspecific interactions, and particularly host–parasite relationships, are a key component of ecosystem stability and their alteration could result in major changes in energy flow.

中文翻译：

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尽管有盐分污染，但绒球仍能操纵伽玛氏虫的行为

1. 淡水生态系统的盐污染是对生物多样性的主要威胁，特别是对自由生存物种及其相关寄生虫之间相互作用的威胁。棘头虫寄生虫能够改变其中间宿主的表型以达到最终宿主，但是该过程可能会受到盐污染的影响，从而损害了该寄生虫的生存。
2. 我们根据三种两足动物的行为：流水覆盖的距离，趋光性和地趋性，实验性地评估了盐对其中间宿主两栖动物Gammarus pulex的寄生虫Pomphorhynchus laevis扩展表型的影响。我们假设：（1）盐污染对未感染的γ-内酰胺类的行为有负面影响，并且（2）尽管有这种污染，但拉美假单胞菌仍可以保持操纵宿主的能力。
3. 与未感染的两栖类相比，在感染或盐污染的水中，这三种两栖类动物的行为均被P. laevis所改变：被感染的G. pulex覆盖的距离更远，憎光性更强，对水表面的吸引更大。然而，盐度减小了被流动的水覆盖的距离，并且增加了对未感染和感染的G.pulex的水表面的吸引力。对于趋光性行为，与对照水相比，P。laevis增强了在盐污染水中的这种操纵能力。
4. 咸水la仍然可以操纵其中间宿主在盐污染水中的行为。尚无棘头para寄生虫在污染压力下能够操纵其中间宿主。营养性相互作用似乎不受盐污染的影响，但不受寄生虫传播至其最终宿主的机会的影响。
5. 我们的研究表明，在某些淡水生态系统中化学污染物浓度不断增加的情况下，应更多考虑复杂的生命周期寄生虫引起的行为改变。种间相互作用，尤其是宿主与寄生虫的关系，是生态系统稳定性的关键组成部分，它们的改变可能导致能量流的重大变化。