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Varying disease-mediated selection at different life-history stages of Atlantic salmon in fresh water.

ABSTRACT: Laboratory studies on associations between disease resistance and susceptibility and major histocompatibility (MH) genes in Atlantic salmon Salmo salar have shown the importance of immunogenetics in understanding the capacity of populations to fight specific diseases. However, the occurrence and virulence of pathogens may vary spatially and temporally in the wild, making it more complicated to predict the overall effect that MH genes exert on fitness of natural populations and over several life-history stages. Here we show that MH variability is a significant determinant of salmon survival in fresh water, by comparing observed and expected genotype frequencies at MH and control microsatellite loci at parr and migrant stages in the wild. We found that additive allelic effects at immunogenetic loci were more likely to determine survival than dominance deviation, and that selection on certain MH alleles varied with life stage, possibly owing to varying pathogen prevalence and/or virulence over time. Our results highlight the importance of preserving genetic diversity (particularly at MH loci) in wild populations, so that they have the best chance of adapting to new and increased disease challenges as a result of projected climate warming and increasing aquaculture.

SUBMITTER: de Eyto E

PROVIDER: S-EPMC3352546 | biostudies-other | 2011 Nov

REPOSITORIES: biostudies-other

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Varying disease-mediated selection at different life-history stages of Atlantic salmon in fresh water.

de Eyto Elvira E McGinnity Philip P Huisman Jisca J Coughlan Jamie J Consuegra Sofia S Farrell Killian K O'Toole Ciar C Tufto Jarle J Megens Hendrik-Jan HJ Jordan William W Cross Tom T Stet Rene J M RJ

Evolutionary applications 20110704 6

Laboratory studies on associations between disease resistance and susceptibility and major histocompatibility (MH) genes in Atlantic salmon Salmo salar have shown the importance of immunogenetics in understanding the capacity of populations to fight specific diseases. However, the occurrence and virulence of pathogens may vary spatially and temporally in the wild, making it more complicated to predict the overall effect that MH genes exert on fitness of natural populations and over several life- ...[more]

PMID: 25568020

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Project description:The aim of this experiment was to explore transcriptomic changes in the gills of Altantic salmon (Salmo salar) following a model lab based parr smolt transformation from fresh water (FW) to salt water (SW). The process of smoltification (migration from FW to SW) is stimulated by long day photoperiod, which acts on the tissue-specific levels of active thyroid hormone (triiodothyronine, T3) through the expression of thyroid hormone type 2 deiodinase (dio2), responsible for conversion of inactive thyroxine (T4) to T3. To gain insight into the functional significance of dio2 induction, we performed a SW-challenge experiment in which we inhibited dio2 activity by addition of iopanoic acid (IOP) to the SW. We also assessed the ability of co-treatment with T3 to override IOP effects. Juvenile fish maintained in FW were subjected to a standard smolt photoperiod regime known to stimulate smoltification, after which they were randomly allocated to one of the four treatments: SW, SW+IOP, SW+IOP+T3 and FW as a control. Fish (n = 8-10 per treatment) were exposed to these conditions for 6 h and then sacrificed to obtain gill tissue for microarray analysis, carried out using a custom-designed Agilent oligonucleotide microarray platform Salar_2 (one glass slide with 4 x 44K arrays, Agilent design ID: 025520, array design A-MEXP-2065), developed and validated for Atlantic salmon (for details, see specific protocols) . In total, 36 hybridisations were performed on gills from individual fish, with 8-10 replicate fish per treatment. We identified 1939 genes whose expression was significantly increased or decreased by transfer from FW to SW. For a subset of 259 genes, this SW response was abolished if IOP was added to the SW, but maintained if T3 was also present during IOP treatment. This group of genes constitutes a candidate list, for which SW-inducibility appears to be dependent on locally mediated changes in gill T3 availability. The results of this experiment have been submitted for publication in Current Biology and are currently under review.

Project description:BackgroundFor decades, linkage mapping has been one of the most powerful and widely used approaches for elucidating the genetic architecture of phenotypic traits of medical, agricultural and evolutionary importance. However, successful mapping of Mendelian and quantitative phenotypic traits depends critically on the availability of fast and preferably high-throughput genotyping platforms. Several array-based single nucleotide polymorphism (SNP) genotyping platforms have been developed for genetic model organisms during recent years but most of these methods become prohibitively expensive for screening large numbers of individuals. Therefore, inexpensive, simple and flexible genotyping solutions that enable rapid screening of intermediate numbers of loci (approximately 75-300) in hundreds to thousands of individuals are still needed for QTL mapping applications in a broad range of organisms.ResultsHere we describe the discovery of and application of insertion-deletion (INDEL) polymorphisms for cost-efficient medium throughput genotyping that enables analysis of >75 loci in a single automated sequencer electrophoresis column with standard laboratory equipment. Genotyping of INDELs requires low start-up costs, includes few standard sample handling steps and is applicable to a broad range of species for which expressed sequence tag (EST) collections are available. As a proof of principle, we generated a partial INDEL linkage map in Atlantic salmon (Salmo salar) and rapidly identified a number of quantitative trait loci (QTLs) affecting early life-history traits that are expected to have important fitness consequences in the natural environment.ConclusionsThe INDEL genotyping enabled fast coarse-mapping of chromosomal regions containing QTL, thus providing an efficient means for characterization of genetic architecture in multiple crosses and large pedigrees. This enables not only the discovery of larger number of QTLs with relatively smaller phenotypic effect but also provides a cost-effective means for evaluation of the frequency of segregating QTLs in outbred populations which is important for further understanding how genetic variation underlying phenotypic traits is maintained in the wild.

Dataset Information

Varying disease-mediated selection at different life-history stages of Atlantic salmon in fresh water.

Publications

Varying disease-mediated selection at different life-history stages of Atlantic salmon in fresh water.

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