Quantitative Trait Loci (QTL) Associated with Resistance to a Monogenean Parasite (<i>Benedenia seriolae</i>) in Yellowtail (<i>Seriola quinqueradiata</i>) through Genome Wide Analysis

<div><p>Benedenia infections caused by the monogenean fluke ectoparasite <i>Benedenia seriolae</i> seriously impact marine finfish aquaculture. Genetic variation has been inferred to play a significant role in determining the susceptibility to this parasitic disease. To evaluate the genetic basis of Benedenia disease resistance in yellowtail (<i>Seriola quinqueradiata</i>), a genome-wide and chromosome-wide linkage analyses were initiated using F₁ yellowtail families (n = 90 per family) based on a high-density linkage map with 860 microsatellite and 142 single nucleotide polymorphism (SNP) markers. Two major quantitative trait loci (QTL) regions on linkage groups Squ2 (<i>BDR-1</i>) and Squ20 (<i>BDR-2</i>) were identified. These QTL regions explained 32.9–35.5% of the phenotypic variance. On the other hand, we investigated the relationship between QTL for susceptibility to <i>B. seriolae</i> and QTL for fish body size. The QTL related to growth was found on another linkage group (Squ7). As a result, this is the first genetic evidence that contributes to detailing phenotypic resistance to Benedenia disease, and the results will help resolve the mechanism of resistance to this important parasitic infection of yellowtail.</p></div

Localization of significant markers for Benedenia disease resistance in linkage group Squ2F and Squ20F with family A.

<p>Squ(linkage group)F; marker distance in female map. (A) Squ2F, (B) Squ20F. Map positions and LOD scores are based on a simple interval mapping QTL analysis using the software MapQTL 5. Marker absolute map distances are given in (cM). 95% confidence probability LOD support interval was indicated as Gray bold line. Horizontal lines across each plot indicate LOD siginificance threshold, <i>P_g</i>; genome-wide significance threshold.</p

Significant markers for Benedenia disease resistance multiple-QTL model mapping in linkage group Squ2F and Squ20F with family A.

<p>Squ(linkage group)F; marker distance in female map. (A) Squ2F, (B) Squ20F. This figure was described using by MapQTL 5.</p

Significant markers for Benedenia disease resistance using Kruskal–Wallis analysis with A and B families.

<p>Signif.; Significance levels:</p>*<p><0.1</p>**<p><0.05</p>***<p><0.01</p>****<p><0.005</p>*****<p><0.001</p>******<p><0.0005</p>*******<p><0.0001.</p><p>NS; not significant, -; not informative in this locus.</p><p>Squ(linkage group)F; F is dam allele in female linkage group. Squ(linkage group)M; M is sire allele in male linkage group.</p

Between fish size and number of parasites in pairwise Pearson correlations.

<p>Values in bold are different from a significance level <i>P</i> = 0.001.</p

Simple interval mapping results of the fish sizes in linkage group 7 and 17 in family A.

<p>Locus; marker name, LOD; Lod scores, % Var; percent of variance explained. Effect; estimated effect. Squ(linkage group)F; F is dam allele in female linkage group. Values in bold are LOD max in peak of each QTL, marker position and each value.</p

Multiple QTL model mapping results of the significant markers for Benedenia disease resistance in linkage group 2 and 20 in family A.

<p>Locus; marker name, LOD; Lod scores, % Var; percent of variance explained, Effect; estimated effect. Squ(linkage group)F; F is dam allele in female linkage group. Values in bold are LOD max in peak of each QTL marker position and each value.</p