Environmental and Genetic Sex Determining Mechanisms in Fishes

Abstract

Teleost fishes are the most speciose group of vertebrate animals, and their study has been fundamental to understanding the mechanisms underlying sex determination, development, physiology, and evolution. Teleosts display extraordinary diversity in a variety of phenotypes, with sexual patterns and determination mechanisms being no exception. Sexual patterns range from familiar male–female gonochorism to various forms of hermaphroditism, including systems where individuals undergo functional sex change over their life cycle, or are capable of self-fertilization. There is also considerable variety in how gonochoristic species determine sex, with mechanisms using social, environmental, and genetic inputs to direct sexual development. Within genetic sex determination systems, there is additional diversity, with monogenic and polygenic systems found in various chromosomal contexts. Here, we review the above diversity and describe how it has revealed broad mechanistic and evolutionary insights into sexual phenotypes. We further discuss why fish display such amazing diversity in sex determination systems and how the necessary evolutionary transitions producing that diversity may have taken place.