Gonadal transcriptome analysis of the effects of temperature on European sea bass (Dicentrarchus labrax) sex ratios

Abstract

The European sea bass (Dicentrarchus labrax) is a gonochoristic species with a polygenic sex determination system with environmental influences. Thus, elevated temperatures can alter population sex ratios by masculinizing fish that otherwise would have developed as females. In the present study, sea bass larvae were exposed to either natural or elevated temperature, the latter expected to induce the male pathway in some of the animals, followed by facultative Estradiol treatment to induce feminization. Growth and sex ratios were determined and samples taken for gene expression analysis. A custom-made microarray was used to determine profiles of gene expression in the gonads of putative females, which were identified as the individuals with the highest cyp19a expression, a marker of female differentiation. Sex ratio analysis of eleven-month-old sea bass showed twice as males in the high temperature group as compared to the low temperature group, while Estradiol treated fish were essentially all females. Microarray analysis of females from these groups, showed 589 differentially expressed genes when comparing high versus low temperature groups (461 up regulated and 128 down-regulated) including genes important for reproduction such as the anti-Müllerian hormone, the transcription factor dmrt1 or the gonadotropin-releasing hormone. Together, these results help to understand the changes brought by elevated temperatures and their connection with resulting sex ratios, a relevant issue under both an aquaculture context and in a global change scenario