Increasing usage of non-medicinal methods (NMMs) to control sea louse infestations on salmon farms has raised questions about whether sea lice may be able to evolve tolerance of NMMs. Of particular concern is the potential for sea lice to evolve freshwater tolerance as a result of freshwater treatments. Wild trout and some juvenile salmonids swim into freshwater to control infestations and regain ionic balance after disruption by sea lice; freshwater tolerance would compromise this potentially adaptive behavior. Here we evaluated the potential for freshwater tolerance to evolve in the sea louse Lepeophtheirus salmonis. When exposed to low-salinity water, parasitic stages of sea lice are able to osmoregulate through the host, while larval planktonic stages are not. Transcriptomic work suggests that sea lice mount a costly polygenic stress response when exposed to brackish water. The population structure of sea lice is panmictic in both the Pacific and Atlantic, making it conducive to rapid evolutionary responses. It is unknown how much heritable genetic variation these panmictic populations have for freshwater treatments. While usage of freshwater treatments on wellboats is increasing, it is unclear whether the freshwater itself is a strong selective force; during the freshwater exposure, sea lice can die from physical disruption during pumping and filtration on the wellboat. Future studies are advised to quantify the heritable variation in freshwater tolerance in sea louse populations, characterize mechanisms for freshwater tolerance in planktonic and attached sea lice, and assess the risk of freshwater tolerance evolution under different management strategies.

中文翻译：

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评估由于鲑鱼养殖中的淡水处理而导致海虱进化出淡水耐受性的潜力

越来越多地使用非药物方法 (NMM) 来控制鲑鱼养殖场的海虱侵扰，引发了海虱是否能够进化出对 NMM 的耐受性的问题。特别令人担忧的是，海虱可能会因淡水处理而进化出对淡水的耐受性。野生鳟鱼和一些幼年鲑鱼游入淡水以控制虫害并在被海虱破坏后恢复离子平衡；淡水耐受性会损害这种潜在的适应性行为。在这里，我们评估了海虱 Lepeophtheirus Salmonis 进化出淡水耐受性的潜力。当暴露于低盐度水时，海虱的寄生阶段能够通过宿主进行渗透调节，而浮游幼虫阶段则不然。转录组学研究表明，海虱在暴露于微咸水中时会产生代价高昂的多基因应激反应。海虱的种群结构在太平洋和大西洋都是混乱的，使其有利于快速进化反应。尚不清楚这些瘟疫种群对淡水处理有多少可遗传的遗传变异。虽然淡水处理在井船上的使用正在增加，但尚不清楚淡水本身是否具有很强的选择力；在淡水暴露期间，海虱可能因井船上抽水和过滤过程中的物理破坏而死亡。建议未来的研究量化海虱种群淡水耐受性的遗传变异，描述浮游和附着海虱对淡水耐受性的机制，