Innate antiviral-like immune responses differ among divergent European and North American farmed and wild Atlantic salmon (Salmo salar) and their hybrids

Dove, Sindy (2022) Innate antiviral-like immune responses differ among divergent European and North American farmed and wild Atlantic salmon (Salmo salar) and their hybrids. Masters thesis, Memorial University of Newfoundland.

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Abstract

This thesis involved a study of the effect of North American (NA) farmed, European origin (EO) farmed, wild, and related hybrid cross types on the innate antiviral-like immune response in Atlantic salmon (Salmo salar). Since the 1970s, millions of farmed salmon have escaped causing concern about how interbreeding with wild salmon may affect wild populations. Farmed and wild salmon differ genetically, yet the immune responses of farmed-wild hybrids are not well understood. In Newfoundland, permission has been granted to start farming an EO strain in addition to the current NA strain from the Saint John River. As these strains differ genetically and geographically, there is concern about potential differences in immune responses. Hence, I used real-time quantitative polymerase chain reaction (qPCR) with head kidney templates to measure expression of seventeen antiviral and other immune-relevant biomarker genes (i.e., dhx58, gig1a, helz2, ifna, ifng, irf1a, irf7b, isg15a, mxb, pgds, rsad2a, rsad2b, stat1a, stat1c, tlr3, tlr7, and 5loxb) to assess the innate antiviral-like immune responses [i.e. to intraperitoneal (IP) injection with polyriboinosinic polyribocytidylic (pIC)] of six different Atlantic salmon cross types including pure crosses (i.e. NA, EO, and local Northeast Placentia River Wild) and three related hybrid crosses. Cross type abbreviations are as follows: pure Wild; pure European farmed (Farm.EO); pure North American farmed (Farm.NA); wild female crossed with Farm.EO male (Hyb.EO w♀); Farm.EO female crossed with wild male (Hyb.EO F♀); and Farm.NA female crossed with wild male (Hyb.NA F♀). At a basal transcript expression level, only one gene (pgds) showed significant cross type differences, where Hyb.NA F♀ had significantly higher expression than the Wild and Hyb.EO F♀. After pIC injection, fifteen of the seventeen target genes (i.e. all except pgds and 5loxb) were significantly upregulated. In addition, there were significant cross type differences in transcript expression of ifna, isg15a, rsad2a, and rsad2b 24 hours post-injection, but only for pIC-injected fish and not the control fish (i.e., sterile phosphate buffered saline injected). The transcript expression of ifna was significantly higher in Farm.EO compared to Wild, Hyb.EO F♀, and Hyb.NAF♀, and also higher in Farm.NA than Wild. The transcript expression of both isg15a and rsad2a was significantly higher in Farm.EO and Hyb.EO W♀ than Wild and Hyb.NA F♀. Lastly, the transcript expression of rsad2b was significantly higher in Hyb.EO W♀ than Wild. This experiment identified important differences in innate antiviral-like response among wild, farmed and related hybrid Atlantic salmon. The results from this study support the hypothesis that interbreeding of wild and escaped farm salmon may modulate the innate immune responses of the hybrid progeny compared with the wild parents. They also suggest that hybridization may not negatively impact the innate immune response in Atlantic salmon and therefore interbreeding resulting from escape events may not pose a threat to the innate immune response of wild populations.

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