SEXUAL LABILITY IN TELEOSTS - DEVELOPMENTAL FACTORS

Among vertebrates there is wide variation in the degree to which sexual differentiation is developmentally buffered, or canalized. In birds, and particularly in mammals, gonadogenesis occurs early in development and without a significant contribution from the environment. In contrast, sexual development in teleosts is protracted and plastic. Here I consider this lability in the context of the developmental processes underlying sex differentiation in teleosts, and contrast these processes with those in other vertebrate taxa. One fundamental difference in teleost sexual differentiation from that of tetrapods may be in the developmental polarity of the brain-pituitary-gonadal axis. In mammals the gonads differentiate early and affect, through the release of steroid hormones, the sexual differentiation of the brain. It is proposed here that in teleosts the brain is the initial site of sexual differentiation, and that the pattern of differentiation in the brain determines the fate of the gonads.