Gilthead seabream (Sparus aurata L.), is an important marine foodfish in the
Mediterranean aquaculture. Although sex determination at age and/or at body weight
are universally critical life history traits shaped by natural selection, their genetic
basis is largely and universally unknown. Herein, we perform a partial-genome scan
to map quantitative trait loci (QTL) affecting body weight and sex in this sequential
hermaphrodite species. Our previous research has shown the existence of two
significant, at a chromosome-wide level, QTL in linkage group 21. The current study
significantly extends (i.e. partial genome scan) the previous genotypic data set to a
more thorough investigation of the genetic architecture for the above traits. Fish from
ten paternal half-sib families were included and 74 (52 genotyped for the purpose of
this study and 22 previously genotyped) informative microsatellite markers were used
to construct nine linkage groups of S. aurata genome with a total sex-average length
of 495.4 cM (Kosambi) and mean marker interval of 7 cM. Interval mapping by linear
regression was applied and extended to a multiple-QTL analysis to increase mapping
power. In total, four growth-related QTL (two chromosome-wide and two genomewide)
were found and six QTL related to sex determination (three pairs in three
different LGs) were detected under the two-QTL model of analysis (two
chromosome-wide and one genome-wide). The proportion of phenotypic variation
explained by the body weight QTL ranged from 9.3 to 17.2 %, showing their potential
for use in marker-assisted selection (MAS). Three linkage groups exhibited
significant evidence, chromosome- or genome-wide, for QTL affecting both growth
and sex, suggesting that the two traits are genetically correlated to some extent in
seabream. The obtained results offer solid ground to investigate the structure and function
of the genomic regions involved in the mechanisms of sex reversal, and to elucidate the complex
mechanistic of the sex determination process and its evolution.
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