Plasticity of brain sexual dimorphism as revealed by sex changing fish.

Sex determination in coral reef fish is highly plastic, with many species displaying socially controlled sequential hermaphroditism. In these species, social hierarchy cues trigger sex change, initiating transformations in neuroanatomy, physiology, morphology, and behavior. The process begins in the brain, where shifts in dominance status alter cortisol release and neuromodulator signaling, including dopamine and arginine vasotocin. Radial glia detect these changes and modulate local estradiol synthesis via brain aromatase production that in turn influences neurogenesis and gene expression in multiple types of glia and neurons involved in pituitary-gonadotroph regulation. The altered gonadotroph control directs the gonadal transformation. Mechanistically, protogyny (female-to-male) typically occurs faster than protandry (male-to-female), with differences in the order of behavioral, gonadal, and morphological changes. Understanding these processes in sex-changing fish provides valuable insights into the neural and endocrine mechanisms underlying reproductive plasticity, with broader implications for neuroendocrinology and the evolution of sex differences in vertebrates.