Serial adult sex change involves rapid and reversible changes in forebrain neurochemistry

SPECIES with multiple sexual phenotypes provide novel insights into neuroendocrine mechanisms underlying vertebrate sexuality. Many fish species are capable of socially mediated sex reversal: the marine goby (Trimma okinawae) is one of only four species known to change sex more than once and in either direction. We have demonstrated that socially mediated serial sex change involves significant and reversible changes in the size of arginine vasotocin-producing forebrain cells. Sex-specific mating and parental behavior also change during sex reversal: both are regulated by the vasotocin/vasopressin peptide family in vertebrates. These neural and behavioral changes are correlated with modifications in gonad form and function, the form of the sexually dimorphic genital papilla, and the presence of an active male accessory gonadal structure. The speed, reversibility, and extent of these changes in adult sexual phenotype is remarkable relative to the rigid nature of these characteristics in many vertebrates.