Sexual plasticity in bony fishes: Analyzing morphological to molecular changes of sex reversal

Abstract

Sex reversal is one of the characteristic properties of sexual plasticity in bony fishes wherein both natural and induced sex change happens at various stages of life cycle in different species. Sex determination in gonochoristic species is genetically regulated, wherein the same sex is retained throughout their life span whereas hermaphrodites change their sex during development or adulthood. In sequential hermaphrodites, serial sex change occurs at different points of life cycle. Concurrently, synchronous hermaphrodites function as both the sexes during spawning. Other variables like temperature, pH and social factors can trigger sex reversal in teleost. Sex reversal through gene mutations and chemicals/hormones, including sex steroids, can be induced mostly at early developmental stages but natural sex reversal can occur at any time. Sex reversal mechanism shows morphological to molecular changes, which are ideal for identification of sex-specific gene markers. In fact, gonadal transdifferentiation occurs at the molecular level through differential expression of transcription factors and steroidogenic enzyme genes vis-a-vis hormones, thereby imparting phenotypic or structural changes. In addition, brain shows sexual dimorphism which is mostly consequential to gonadal sex development and occasionally either causative. The major breakthrough in this line is the identification of sex determining genes such as dmy/dmrt1Yb, gsdfY, sox3 in the Japanese medaka and amhY in Patagonian pejerrey. Incidentally, the induction of mono-sex population by favouring one sex due to sex-specific differences in growth is an important economic boom for aquaculture. This review comprehensively highlights key molecular factors involved in natural and induced sex reversal conditions to illustrate teleostean sexual plasticity and its application perspectives.