Differential expression of reproduction and sex-determining genes in the gonads of genotypic and temperature-induced males of gibel carp (Carassius gibelio)

Sex in vertebrates is commonly determined by genotype and environmental conditions, such as temperature. A few species display intermediate systems, combining sex chromosomes with temperature effect. This phenomenon has been reported in gibel carp (Carassius gibelio), an invasive cyprinid fish whose invasiveness is linked to the combination of sexual and asexual reproduction. Here, we compared gonadal transcriptomes between genotypic males and temperature-induced males of C. gibelio, focusing specifically on genes related to reproduction. Many meiosis and male differentiation pathways were common to genotypic and temperature-induced males. However, the underrepresentation of reproduction- and spermatogenesis-related terms in temperature-induced males suggests reduced reproductive abilities. Our study further highlights differential regulation of key genes related to male differentiation, steroid hormone signalling, meiosis, spermatogenesis, flagellar function, and sperm-egg interaction. In particular, induced males strongly overexpressed the key sex differentiation regulator hsd17b2 and slightly overexpressed the meiotic gene mnd1, while genotypic males overexpressed sox8a, cyp19a1a, and the crucial fertilization gene izumo. Our study highlights the importance of males in the transition from asexual to sexual reproduction in this species and contributes to understanding the molecular mechanisms underlying the reproductive plasticity and invasiveness of C. gibelio in Europe.