Identification of genetic markers associated with Gyrodactylus salaris resistance in Atlantic salmon Salmo salar

Abstract

Gyrodactylus salaris Malmberg, 1957 is a freshwater monogenean ectoparasite of salmonids, first recorded in Norway in 1975 and responsible for extensive epizootics in wild Atlantic salmon Salmo salar L. The susceptibility of different populations of Atlantic salmon to G. salaris infection differs markedly, with fish from the Baltic being characterised as relatively resistant whereas those from Norway or Scotland are known to be (extremely) susceptible. Resistance to Gyrodactylus infection in salmonids has been found to be heritable and a polygenic mechanism of control has been hypothesised. The current study utilises a 'Quantitative trait loci' (QTL) screening approach in order to identify molecular markers linked to QTL influencing G. salaris resistance in B1 backcrosses of Baltic and Scottish salmon. Infection patterns in these fish exhibited 3 distinct types; susceptible (exponential parasite growth), responding (parasite load builds before dropping) and resistant (parasite load never increases). B1 backcross fish were screened at 39 microsatellite markers and single marker-trait associations were examined using general linear modelling. We identified 10 genomic regions associated with heterogeneity in both innate and acquired resistance, explaining up to 27.3% of the total variation in parasite loads. We found that both innate and acquired parasite resistance in Atlantic salmon are under polygenic control, and that salmon would be well suited to a selection programme designed to quickly increase resistance to G. salaris in wild or farmed stocks. KEY WORDS: Gyrodactylus salaris · Atlantic salmon · Resistance · Linkage mapping · Quantitative trait loci Resale or republication not permitted without written consent of the publisherDis Aquat Org 71: [119][120][121][122][123][124][125][126][127][128][129] 2006 Western Atlantic Ocean, the Eastern Atlantic Ocean and the Baltic (Stahl 1987, Bakke et al. 1990. Within these groups the species comprise multiple, genetically differentiated and, to a large extent, reproductively isolated river populations (Stahl & Hindar 1988). There is virtually no migration of fish from the Baltic into the Eastern Atlantic, or vice versa (Christensen & Larsson 1979). Population level genetic heterogeneity in resistance within and between salmon populations may thus be important in determining whether an epizootic takes place in a particular river (Pickering 1987), and for the future development of stocks resistant to the parasite (Bakke et al. 1999).Most species of freshwater fish seem to be more susceptible to attack from parasites to which they have not been previously exposed (Dobson & May 1987, Bakke et al. 1990). Heterogeneity in susceptibility of different salmon stocks, and of individuals of the same stock, to Gyrodactylus salaris has been noted in a number of studies, with fish from the Baltic being less susceptible than those of the Eastern Atlantic (Bakke et al. 1990, Bakke & MacKenzie 1993, Jansen & Bakke 1993a,b, Rintamäki-Kinnunen & Valtonen 1996, Cable et al....

Major Quantitative Trait Loci Affect Resistance to Infectious Pancreatic Necrosis in Atlantic Salmon (Salmo salar)

“…mbb.sfu.ca/GRASPlinkage.html), which combines molecular marker and mapping data from the Genomic Research on Atlantic Salmon Project (GRASP) (http:// grasp.mbb.sfu.ca/), the Salmon Genome Project (SGP) (http:/ /www.salmongenome.no/cgi-bin/sgp.cgi), and the European Union collaborative SALMAP project (http:/ / www.salmongenome.no/cgi-bin/sgp.cgi). These maps have facilitated the detection of QTL in salmon affecting body weight and condition factor (Reid et al 2005), while molecular markers have also been linked to disease resistance against infectious salmon anemia (ISA) (Grimholt et al 2003;Moen et al 2004bMoen et al , 2007, furunculosis (Grimholt et al 2003), and the ectoparasite Gyrodactylus salaris (Gilbey et al 2006). Furthermore, in the closely related rainbow trout, two QTL have been identified with a highly significant effect on freshwater IPN resistance in a backcross family (Ozaki et al 2001).…”

Genotypic and phenotypic correlates with proliferative kidney disease-induced mortality in Atlantic salmon

“…Also, due to the outbred nature of the families, it would be expected that most parents would not be informative for most markers and that the associations, therefore, were family-specific. Furthermore, it points to polygenic control of disease resistance, as found in other studies (Gilbey et al 2006, Barroso et al 2008, with the likelihood that loci with useful variation in mounting an immune response vary among families.…”

“…A basic, single marker-single linkage group approach was used (Gilbey et al 2006), whereby microsatellite markers were chosen to cover each linkage group of the linkage map of Gilbey et al (2004), along with further markers from the linkage groups identified in SALMAP (www.asalbase.org/ sal-bin/index) and Moen et al (2008). Furthermore, a growth hormone gene marker, not mapped to any identified linkage group, was screened to assess association with this region of the genome.…”

Current Advances in Functional Genomics in Aquaculture

“…Bacteria disease for which QTL resistance traits have been identiied include coldwater disease in rainbow trout [187], Aeromonas hydrophila in rohu (Labeo rohita) [188], Vibrio anguillarum in Japanese lounder [189], Flavobacterium psychrophilum in rainbow trout [190] and pastuerellosis in Gilhead seabream [191]. As for parasitic diseases, QTL resistance traits have been identiied for Gyrodactylus salaris in Atlantic salmon [192] and Monohenean parasite (Benedenia seriolae) in Yellow tail (Seriola quinqueradiata) [193].…”