Salmon farming is one of the most valuable forms of aquaculture worldwide1, but its economic and ecological sustainability is continuously threatened by the salmon louse (Lepeophtheirus salmonis)2. This ectoparasitic copepod transfers between farmed and wild salmon throughout the northern hemisphere, and can impact hosts at the cellular, individual, and population levels2. In many parts of the world, the preferred method of control for salmon lice has been an in-feed parasiticide called emamectin benzoate (EMB; trade name SLICE)3, but rapidly evolved resistance has contributed to the chemical being used more sparingly and in combination with many other treatments in Atlantic-Ocean farming regions4,5,6.
Strongholds Of Resistance Pdf 19
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In stark contrast to the situation in the Atlantic, salmon lice in the Pacific Ocean appeared to have avoided widespread evolution of EMB resistance7 despite EMB being virtually the only treatment option used in the region until roughly 2017. Canada is the main salmon-farming country in the north Pacific, and genetic evidence has revealed only localized ephemeral resistance here8, potentially due to the large wild Pacific salmon populations that act as untreated refuges for susceptible lice7, 9. Pacific Canada is unique globally for having substantial populations of both farmed and wild salmon1. Management decisions for salmon aquaculture in Pacific Canada are thus unmatched worldwide for their potential impacts on the natural systems that depend on salmon.
Resistance to EMB is typically identified through bioassays in which hundreds of salmon lice, grouped by sex, are placed in baths of different concentrations along a gradient of EMB for 24 hours10, which differs from the host-dependent exposure that lice on farms experience due to in-feed administration of EMB. For each bioassay, the effective concentrations at which 50% of lice survive (EC50) are calculated, and if EC50 values increase over time then EMB resistance in salmon lice is inferred. Male salmon lice are generally more resistant to EMB than females, for reasons that are unclear11. Salmon-farming companies in Pacific Canada regularly conduct bioassays to assess EMB sensitivity of lice on their farms, but the raw data have never been publicly available. Summarized bioassay data were last made available in 201210.
Here, we assess whether Pacific salmon lice have evolved EMB resistance by analyzing bioassay, treatment, and salmon-louse count data from 2010 to 2021 in the Broughton Archipelago (BA), British Columbia (BC) (Fig. 1), long a focus of salmon-farm research and management in the Pacific12.
Increasing trends in: (A) salmon-louse resistance to emamectin benzoate (EMB), and (B) relative salmon-louse counts after EMB treatment. Points in panel (A) represent the effective concentrations required to kill 50% of male (blue) or female (red) salmon lice (EC50) in bioassays. Points in panel (B) show the relative post-treatment counts (i.e., the post-treatment counts divided by the pre-treatment counts). Lines depict the mean predictions from the top-ranked models. Error bars and shaded regions give 95% confidence intervals.
The apparently resistant salmon lice from the recent bioassays are obvious candidates for follow-up genetic analyses. Such genetic work is beyond the scope of the present study, in part because the lice were not retained by the salmon-farming companies to the First Nations. Although there are still no diagnostic genetic tests for EMB resistance of Pacific salmon lice, a rare louse genotype (with characteristic single nucleotide polymorphisms) was recently linked to ephemeral EMB tolerance in BC8. These signs of nascent resistance, evident in samples from nearly a decade ago, strongly suggest that the trends we document here have a genetic basis and are not merely plastic changes. Our results highlight the need for assessments of the frequency of this rare genotype, ideally with full public reporting and independent verification, as an integral part of EMB bioassays until a full diagnostic test is developed.
While this is the first published account with evidence for the evolution of EMB resistance in the Pacific Ocean, it seems quite likely that industry and the federal regulator have been aware of this emerging issue for some time. EMB tolerance was reported in 2013 as a localized and short-lived phenomenon in one farm in BC10, and again in 20188, which presumably raised concerns internally about resistance becoming a pervasive problem. Treatment failures8, 13, alternative treatments8, 13, persistently elevated counts14, and concerning bioassays8 have occurred in other parts of Pacific Canada at earlier dates than in the BA. Combined with our findings, this suggests that EMB resistance is widespread and well established in BC. Whether large returns of wild salmon could impart some relief to farms by providing an influx of treatment-susceptible lice will be a situation to monitor over the coming years, but is probably unlikely given the trends we report here across 11 farms.
Despite the local and global forewarnings of EMB resistance, industry was exclusively permitted to use EMB for delousing treatments in the BA until late 2019, a strategy which imposes strong selection and likely resulted in accelerated evolution of resistance15 (but see7, 9). Three additional treatment options (i.e., freshwater baths, hydrogen peroxide baths, and jets of pressurized water) have since been introduced and are now used frequently; these other treatments accounted for 62% of treatments in 2021. With EMB effectiveness declining, industry has had to (and will continue having to) reactively (rather than proactively) diversify its approaches to louse control in order to better align with the integrated pest management strategies used in other countries. A suite of non-chemical preventative methods (e.g., barriers to limit surface interactions between fish and lice) have had promising results elsewhere, and many other chemical, mechanical, and biological treatment options are also available (see review by Coates et al.15). Each of these treatment options has its own drawbacks, however (e.g., resistance to chemotherapeutants4, 15, welfare issues from mechanical treatments16, and pathogen transmission with cleaner fish17), some of which will worsen with climate change, necessitating a diverse set of strategies for louse control.
Until recently, the Pacific Ocean was considered the last stronghold of treatment-susceptible salmon lice7, but our results suggest that resistance has now emerged. EMB resistance in BC could have arisen from depleted wild salmon populations7, 22, ill-advised reliance on a single treatment15, or insufficiently aggressive treatment on the part of farms9, 23, any of which would suggest a failure of management at some level. Whatever the cause, the emergence of resistant salmon lice in the Pacific poses serious challenges for controlling outbreaks to protect wild salmon in the coming years, further exacerbating the negative consequences of lice on salmon predicted in a warming climate24.
Panel A. Linezolid interferes with the positioning of aminoacyl-tRNA by interactions with the peptidyl-transferase center (PTC). Ribosomal proteins L3 and L4 associated with resistance are shown. Panel B. Representation of domain V of 23S rRNA showing mutations associated with linezolid resistance. Position A2503, which is the target of Cfr methylation, is highlighted.
Description: The Popular Front for the Liberation of Palestine-General Command (PFLP-GC) was designated as an FTO on October 8, 1997. The PFLP-GC split from the Popular Front for the Liberation of Palestine in 1968, claiming it wanted to concentrate more on resistance and less on politics. Ahmad Jibril, a former captain in the Syrian army, has led the PFLP-GC since its founding. The PFLP-GC has close ties to both Syria and Iran.
In 2016, the anti-IS coalition achieved important victories in IS-controlled territories, recovering Ramadi in February and Falluja in June.[89] IS consistently surprised coalition forces with its fierce resistance and brutal urban fighting with high civilian casualties.[90] In Iraq, the Iraqi army and local Shia militias cooperated in an effort to take and hold IS territory. The Iraqi army focused on liberating an IS-controlled city, and local Shia militias held and protected the territory after the Iraqi military victory.[91] This allowed the Iraqi army to move to the next battle without leaving recaptured areas unsecured and vulnerable. The Shia militia presence, however, also led to tensions with the mostly Sunni communities that they now patrolled.[92]
After October 2006, AQI focused on the creation of institutional infrastructure for a religious state. It formed the Islamic State of Iraq (ISI) and attempted to rebrand itself as more Iraqi. Though AQI tried to impose order in the regions it controlled, it failed to establish an effective state structure and was becoming weaker due to Sunni resistance and increased American troop presence.[3] By 2007, AQI was too weak to provide security or enforce its extreme interpretation of Sharia law.[4]
Africans across the continent resisted colonial demands and took up arms against European colonizers during World War I. This essay presents three ways of recognizing and analyzing such acts of resistance. First, many Africans refused increased colonial labor demands. Second, religious movements shaped how African peoples interpreted what was happening to their societies once the war in Africa began. Finally, some African polities saw the war as an opportunity to restructure political relationships between themselves and European colonizers.
Understanding why the war years became a fertile period for anti-colonial resistance requires consideration of the longer history of everyday colonialism and the alliances and resentments it produced. Resistance during the war affected societies after the war as well, with colonizers harboring fears that their economic and political goals would be undermined by further rebellions. While 1914-1918 constituted a rupture in certain ways, it also exacerbated longstanding harsh prewar conditions. The postwar period similarly brought new forms of colonial exploitation, on a grander scale, as colonizers consolidated authority and control over African labor. 2ff7e9595c
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