Gonadal gene expression in a fish with genetic and environmental sex determination under thermal and chemical pollution

Understanding the consequences of thermal and chemical variations in aquatic habitats is of importance in a scenario of global change. In ecology, the sex ratio is a major population demographic parameter. Research carried out so far on environmental perturbations on fish sex ratios has usually involved a few model species with a strong genetic basis of sex determination, analyzing juvenile or adult gonads. However, the underlying mechanisms at the time of commitment are poorly understood. The European sea bass has a mixed genetic and environmental sex determination system, which makes it naturally sensitive to environmental cues. Here, we transcriptomically analyzed developing gonads experiencing either testis or ovarian differentiation as a result of thermal and/or estrogen influences. Elevated temperature masculinized genetic females while estrogen exposure resulted in an all-female population. A total of 383 genes were differentially expressed, with an overall downregulation in the expression of genes involved both in testicular and ovarian differentiation in the estrogen-exposed fish achieved by a shutdown of the first steps of steroidogenesis. GO enrichment analysis uncovered affected pathways related to the immune response, xenobiotic metabolism, response to stimulus, signaling and growth. However, once the female phenotype was imposed gonads could continue their normal development, even taking into account that some of the resulting females were fish that otherwise would have developed as males. The data on the underlying mechanisms operating at the molecular level presented here contributes to better understanding the sex ratio response of fish species subjected to a combination of environmental perturbations. Whole gonad transcriptome analysis from 10 individuals: 5 individuals early reared at a low temperature (15°C) and 5 individuals early reared at high temperature (21°C) all of them submitted to a feminizing treatment by Estradiol administration between 90 and 154 days post hatch.