Characterization and refinement of growth related quantitative trait loci in European sea bass (Dicentrarchus labrax) using a comparative approach

The identification of genetic markers for traits of interest for aquaculture, such as growth, is an important step for the establishment of breeding programmes. As more genomic information becomes available the possibility of applying comparative genomics to identify and refine quantitative trait locus (QTLs) and potentially identify candidate genes responsible for the QTL effect may accelerate genetic improvement in established and new aquaculture species. Here we report such an approach on growth related traits in the European sea bass (Dicentrarchus labrax), an important species for European aquaculture. A genetic map was generated with markers targeted to previously identified QTL for growth which reduced distance and improved resolution in these regions. A total of 36 significant QTLs were identified when morphometric traits were considered individually in maternal half sibs, paternal half sibs and sib-pair analysis. Twenty seven new markers targeted to the growth QTLs, obtained by comparative mapping, reduced the average distance between markers from 23.4, 9.1, and 5.8. cM in the previous map to 3.4, 2.2, and 5.2. cM, on linkage group (LG) LG4, LG6 and LG15 respectively. Lists of genes embedded in the QTL - 591 genes in LG4, 234 genes in LG6 and 450 genes in LG15 - were obtained from the European sea bass genome. Comparative mapping revealed conserved gene synteny across teleost fishes. Functional protein association network analysis with the gene products of the 3 linkage groups revealed a large global association network including 42 gene products. Strikingly the association network was populated with genes of known biological importance for growth and body weight in terrestrial farm animals, such as elements of the signaling pathways for Jak-STAT, MAPK, adipocytokine and insulin, growth hormone, IGFI and II. This study demonstrates the feasibility of a comparative genomics combined with functional gene annotation to refine the resolution of QTL and the establishment of hypothesis to accelerate discovery of putative responsible genes. Statement of relevance: This study demonstrates the feasibility of a comparative genomics approach, combined with functional annotation to refine the resolution of QTL and establishment of hypothesis to accelerate discovery of candidate genes. As production of genomic data is becoming more accessible, the implementation of this strategy will rapidly and efficiently provide the tools required for genetic selection in new candidate aquaculture species.