title: Transcriptomic responses to emamectin benzoate in Pacific and Atlantic Canada salmon lice Lepeophtheirus salmonis with differing levels of drug resistance.
abstract: Salmon lice Lepeophtheirus salmonis are an ecologically and economically important parasite of wild and farmed salmon. In Scotland, Norway, and Eastern Canada, L. salmonis have developed resistance to emamectin benzoate (EMB), one of the few parasiticides available for salmon lice. Drug resistance mechanisms can be complex, potentially differing among populations and involving multiple genes with additive effects (i.e., polygenic resistance). Indicators of resistance development may enable early detection and countermeasures to avoid the spread of resistance. Here, we collect sensitive Pacific L. salmonis and sensitive and resistant Atlantic L. salmonis from salmon farms, propagate in laboratory (F1), expose to EMB in bioassays, and evaluate either baseline (Atlantic only) or induced transcriptomic differences between populations. In all populations, induced responses were minor and a cellular stress response was not identified. Pacific lice did not upregulate any genes in response to EMB, but downregulated degradative enzymes and transport proteins at 50 ppb EMB. Baseline differences between sensitive and now resistant Atlantic lice were much greater than responses to exposures. All resistant lice overexpressed degradative enzymes, and resistant males, the most resistant group, overexpressed collagenases to the greatest extent. These results indicate an accumulation of baseline expression differences related to resistance.
authors: Centre for Biomedical Research, Department of Biology, University of Victoria Victoria, BC, Canada ; Institut de Biologie Intégrative et des Systèmes (IBIS), Département de biologie, Université Laval Québec, QC, Canada.
authors: Ben J G
authors: BJ
authors: Sutherland
authors: Hoplite Lab, Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island Charlottetown, PEI, Canada.
authors: Jordan D
authors: JD
authors: Poley
authors: Hoplite Lab, Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island Charlottetown, PEI, Canada.
authors: Okechukwu O
authors: OO
authors: Igboeli
authors: Centre for Biomedical Research, Department of Biology, University of Victoria Victoria, BC, Canada.
authors: Johanna R
authors: JR
authors: Jantzen
authors: Hoplite Lab, Department of Pathology and Microbiology, Atlantic Veterinary College, University of Prince Edward Island Charlottetown, PEI, Canada.
authors: Mark D
authors: MD
authors: Fast
authors: Centre for Biomedical Research, Department of Biology, University of Victoria Victoria, BC, Canada.
authors: Ben F
authors: BF
authors: Koop
authors: Pacific Biological Station Nanaimo, BC, Canada.
authors: Simon R M
authors: SR
authors: Jones
keywords: drug resistance; emamectin benzoate; polygenic resistance; salmon aquaculture; sea lice; transcriptomics