Abstract
Among vertebrates, teleost fish exhibit a considerably wide range of sex determination patterns that may be influenced by extrinsic parameters. However even for model fish species like the zebrafish Danio rerio the precise mechanisms involved in primary sex determination have not been studied extensively. The zebrafish, a gonochoristic species, is lacking discernible sex chromosomes and the sex of juvenile fish is difficult to determine. Sequential protandrous hermaphrodite species provide distinct determination of the gender and allow studying the sex determination process by looking at the mechanism of sex reversal. This is the first attempt to understand the genetic basis of phenotypic variation for sex determination and body weight in a sequential protandrous hermaphrodite species, the gilthead sea bream (Sparus aurata). This work demonstrates a fast and efficient strategy for Quantitative Trait Loci (QTL) detection in the gilthead sea bream, a non-model but target hermaphrodite fish species. Therefore a comparative mapping approach was performed to query syntenies against two other Perciformes, the European sea bass (Dicentrarchus labrax), a gonochoristic species and the Asian sea bass (Lates calcarifer) a protandrous hermaphrodite. In this manner two significant QTLs, one QTL affecting both body weight and sex and one QTL affecting sex, were detected on the same linkage group. The co-segregation of the two QTLs provides a genomic base to the observed genetic correlation between these two traits in sea bream as well as in other teleosts. The identification of QTLs linked to sex reversal and growth, will contribute significantly to a better understanding of the complex nature of sex determination in S. aurata where most individuals reverse to the female sex at the age of two years through development and maturation of the ovarian portion of the gonad and regression of the testicular area. [Genomic sequences reported in this manuscript have been submitted to GenBank under accession numbers HQ021443–HQ021749.]
Highlights
Sex determination is one of the most important mechanisms in biology as well as one of the cornerstones of evolution guaranteeing sexual reproduction
Such pedigree mistakes result in a small loss of Quantitative Trait Loci (QTL) detection power [25] and can be improved when individuals are genotyped with more markers for linkage analysis and QTL mapping purposes
The small presence of females in the progeny was expected, as old males have a much higher potential to go through sex reversal than younger males do, at two years of age only a few male individuals have turned into to the female sex
Summary
Sex determination is one of the most important mechanisms in biology as well as one of the cornerstones of evolution guaranteeing sexual reproduction. Sequential protandrous hermaphrodite species provide distinct determination of the gender and sex determination studies can be performed through the possibility of studying the mechanism of sex reversal. Hermaphrodite fish species can become a target group to study sex determination they are not belonging to the species for which extended genome information is available. Due to the increasing interest in aquaculture fish species, research has been made in their physiology and in molecular biology while the need for genomic resources has been addressed and is developing as for example for the gilthead sea bream Sparus aurata, a sequential protandrous hermaphrodite. Information coming from other fish species, either model species or economically important species can be mapped onto the existing RH and LG map [20] In this manner more targeted QTL scan is performed
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