Résumé
Sex of Nile tilapia is determined genetically by sex chromosomes following an XX/XY system, but temperature can override it. High temperatures >32°C applied during early sex-differentiation can induce a female to male sex reversal producing functional testis and a male reproductive behaviour. The male proportion induced by temperature (the thermosensitivity) is an inherited trait. We treated two genetically different families sired from wild-caught Nile tilapia fish from Lake Kou (Burkina Faso) to 36°C during their sex-differentiating stage. At 90 days post-fertilization, Family K14 had a 90% male proportion whereas, Family K13 only showed 59.8% males. Epigenetic differences in DNA methylation levels persisted in adult ovaries and testis. Our MeDIP-Seq analyses predicted 26,339 CpG islands with presumably low methylation, and identified 77,427 regions of high methylation in K14 and 63,168 regions in K13. Our findings indicate that in contrast to CGI methylation, the bulk methylome of the phenotypically plastic K14 family reacts strongly to temperature increase while the K13 family with low phenotypic plasticity remains stable. We found 964 differentially methylated regions (DMR) between XY males and XX females in the thermosensitive K14 family whereas K13 had 87 DMRs, with differentially expressed genes of histone modifiers and involved in temperature-sensitive pathways.