Effect of high temperatures on sex ratio and differential expression analysis (RNA-seq) of sex-determining genes in from different river basins in Benin.

The high temperature sex reversal process leading to functional phenotypic masculinization during development has been widely described in Nile tilapia () under laboratory or aquaculture conditions and in the wild. In this study, we selected five wild populations of from different river basins in Benin and produced twenty full-sib families of mixed-sex (XY and XX) by natural reproduction. Progenies were exposed to room temperature or high (36.5°C) temperatures between 10 and 30 days post-fertilization (dpf). In control groups, we observed sex ratios from 40% to 60% males as expected, except for 3 families from the Gobé region which showed a bias towards males. High temperature treatment significantly increased male rates in each family up to 88%. Transcriptome analysis was performed by RNA-sequencing (RNA-seq) on brains and gonads from control and treated batches of six families at 15 dpf and 40 dpf. Analysis of differentially expressed genes, differentially spliced genes, and correlations with sex reversal was performed. In 40 dpf gonads, genes involved in sex determination such as , and were upregulated. In 15 dpf brains, a negative correlation was found between the expression of and the reversal rate, while at 40 dpf a negative correlation was found between the expression of , and and positive correlation was found between expression and reversal rate. Ontology analysis of the genes affected by high temperatures revealed that male sex differentiation processes, primary male sexual characteristics, autophagy, and cilium organization were affected. Based on these results, we conclude that sex reversal by high temperature treatment leads to similar modifications of the transcriptomes in the gonads and brains in offspring of different natural populations of Nile tilapia, which thus may activate a common cascade of reactions inducing sex reversal in progenies.