Sex Determination and Differentiation Mechanisms in Aquatic Species

Aquatic organisms exhibit a remarkable diversity of strategies to establish and maintain sexual fate, ranging from strictly genetic systems to those heavily influenced by environmental factors. In many teleost fishes, crustaceans and molluscs, genetic sex determination relies on heteromorphic sex chromosomes or polygenic networks that trigger a cascade of gene expression programmes. Conversely, temperature-dependent sex determination and other environmental cues can override genetic predisposition through epigenetic modifications of key regulatory regions. Following the primary decision, differentiation of gonadal tissue into testes or ovaries and the development of secondary sexual characteristics are orchestrated by hormonal pathways involving enzymes such as aromatase and receptors for androgens and oestrogens. Master sex-determining genes initiate these cascades, while downstream factors refine and stabilise sexual phenotype. Understanding these mechanisms is essential for conservation of vulnerable populations, management of fishery stocks under changing climate regimes and the optimisation of aquaculture for sustainable food production.

Research from Nature Portfolio

Recent work in teleosts has dissected the evolution and functional divergence of androgen receptor paralogues in medaka. This study demonstrates that two teleost-specific androgen receptor ohnologs have partitioned roles in fin morphogenesis, courtship behaviour and reproductive success, despite being dispensable for spermatogenesis. Divergence in gene regulation, protein localisation and downstream regulatory networks after genome duplication has driven phenotypic diversity in male sexual traits. Such findings illuminate how gene duplication can resolve pleiotropy and fuel the evolution of complex sexual characteristics in aquatic vertebrates.

Sex Determination and Differentiation Mechanisms in Aquatic Species publication trend

The graph below shows the total number of articles in sex determination and differentiation mechanisms in aquatic species across all publications each year (not limited to Nature Index journals).

Technical terms

Genotypic sex determination (GSD): a system in which genetic elements such as sex chromosomes dictate sexual fate.

Temperature-dependent sex determination (TSD): a mechanism whereby external temperature during early development influences ultimate sex outcome.

Dosage compensation: processes that equalise expression of genes on sex chromosomes between individuals of different chromosomal sexes.

Master sex-determining gene: the initial genetic switch that commits undifferentiated gonadal tissue to develop as testes or ovaries.

Gene duplication: the generation of extra copies of a gene that can evolve new or specialised functions.

Epigenetics: heritable changes in gene activity that do not involve alterations in the DNA sequence, often mediated by DNA methylation.

Aromatase (cyp19a): the enzyme that converts androgens into oestrogens, crucial for ovarian differentiation.

References

1. Evolutionary differentiation of androgen receptor is responsible for sexual characteristic development in a teleost fish. Nature Communications (2023).
2. DNA Methylation of the Gonadal Aromatase (cyp19a) Promoter Is Involved in Temperature-Dependent Sex Ratio Shifts in the European Sea Bass. PLOS Genetics (2011).
3. A Trans-Species Missense SNP in Amhr2 Is Associated with Sex Determination in the Tiger Pufferfish, Takifugu rubripes (Fugu). PLOS Genetics (2012).
4. A Tandem Duplicate of Anti-Müllerian Hormone with a Missense SNP on the Y Chromosome Is Essential for Male Sex Determination in Nile Tilapia, Oreochromis niloticus. PLOS Genetics (2015).